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Full text of "Integrated Circuits ( How to make them work )"

PRACTICAL HANDBOOK SERIES 



OK 



circuits 

HOW TO MAKE THEM WORK 

R.H. Warring 













Integrated circuits - or ICs - are largely 
replacing transistors in all forms of 
electronic equipment for the home and 
industry. The modern electronics engineer 
automatically adopts them as standard 
practice. This book offers a completely 
practical introduction for the amateur to 
the fascinating world of using ICs, in the 
home or workshop, and turning them into 
working circuits. 

ICs are 'complete' or near-complete 
circuits which normally need only a few 
external components added to produce a 
working electronic device. They are 
extremely compact and efficient in per- 
formance. Due to large-scale manufacture, 
they are also relatively inexpensive. The 
problem for the amateur is knowing 
which IC is suitable for his particular 
needs - and then how to incorporate it 
into a working circuit. The author answers 
these problems by describing the different 
'families' of ICs, how to identify their 
connections, and how they are connected 
to external components to make working 
circuits, usually with only the addition of 
a few resistors and a capacitor or two. 
One of the great advantages of using ICs, 
in fact, is the small total number of 
components usually required and their 
lower total cost (including the IC) 
compared with building a similar circuit 
from separate components. 

There are literally thousands of different 
ICs available today, from simple 'Op- 
Amps' to complete digital circuits. The 
author has selected representative types, 
all of which are readily available, in 
describing and illustrating eighty-four 
working circuits. These range from simple 

ISBN o 7j88 3343 5 




m 




! 



INTEGRATED CIRCUITS 

HOW TO MAKE THEM WORK 



PRACTICAL HANDBOOK SERIES 

Integrated Circuits: How to Make Them Work 
by R. H. Warring 

Clocks and Clock Repairing 
by Eric Smith 



PRACTICAL HANDBOOK SERIES 

INTEGRA TED 
CIRCUITS 

HOW TO MAKE THEM WORK 

by 
R.H. WARRING 



LUTTERWORTH PRESS 
GUILDFORD AND LONDON 



First published 1979 






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ISBN 7188 2343 5 



COPYRIGHT © 1979 R. H, WARRING 

All Rights Reserved. No pan of this publication 
may be reproduced, stored in a retrieval system, 

or transmitted, in any form or by any means, 

electronic, mechanical, photocopying, recording 

or otherwise, without the prior permission of 

Lutterworth Press. Famham Road. Guildford, Surrey. 

Printed in Great Britain by 

Ebenezer Baylis & Son Ltd. 

. The Trinity Press, Worcester, and London 



CONTENTS 

Chapter 

List of Working Circuits to Build 
Preface 

1 . Introduction to Integrated Circuits 

2. General Purpose ICs (Arrays) 

3. Op-Amps 

4. Audio Amplifiers 

5. Heat Sinks 

6. Complete Radio Circuits 

7. Multivibrators 

8. Voltage Regulators 

9 . Electric Motor Speed Com rol 1 ers 

10. Filters 

1 1 . Introducing Digital Circuits 

12. Electronic Organs 

13. Miscellaneous Circuits 
Index 



page 

7 

11 

13 

22 

30 

44 

60 

64 

73 

79 

84 

88 

92 

101 

107 

129 



I 



LIST OFWORKINGCIRCUITS 



Figures 

1.4 IC Radio 

2.2 Voltage Regulator 

2.4 Voltage Regulator 

2.5 Astable Multivibrator 

2.6 High gain Amplifier 

2.7 Constant Current Supply 

2.8 Constant Voltage Supply 

3.2 Op-Amp Adder 

3.3 Non-inverting Adder 

3.4 Inverter 

3.5 Non-inverting Adder 

3.6 Adder /Subtractor 

3.7 Integrator 

3.8 Differentiator 

3.9 Differential Amplifier 

3.10 Log Amplifier 

3.11 Logarithmic Calculator 

3.12 Voltage Follower 

3.13 Voltage-to-Current Converter 

3.14 Currentto-Voltage Converter 

3.15 Op-Amp as Current Source 

3.16 Basic Multivibrator Circuits 

3.17 Simple Schmitt Trigger 

7 



page 
18 
23 
25 
26 
27 
28 
28 
31 
31 
32 
32 
33 
34 
34 
35 
35 
36 
37 
37 
38 
38 
39 
40 



INTEGRATED CIRCUITS 

3.18 Schmitt Trigger 40 

3.19 Capacitance Multiplier 41 

4.1 Single-stage Amplifier (gain 100) 44 

4.2 Single-stage Amplifier (gain 100-200) 45 

4.3 Single-stage Amplifier (gain 80-120) 46 

4.4 Cascaded Amplifier (gain 7000) 46 

4.5 High-gain Cascaded Amplifier (gain 700,000) 47 

4.6 Audio Amplifier 48 

4.9 Audio Amplifier for 4-ohm Loudspeaker 52 

4.10 10-watt Amplifier 53 

4. 12 Stereo Amplifier 56 

4.13 Powerful Bridge Amplifier 57 

4.14 Simp!e2x6 watt Stereo Amplifier 58 

6.1 Basic Working Radio 65 

6.2 IC Radio with Transistor Amplifier 65 

6.3 Complete High-quality IC Radio 67 

6.4 AM/FM Receiver 68 

6.5 FM Receiver Front End 69 

7.1 Square Wave Oscillator 73 

7.2 Pulse Generator 74 

7.3 Audio Tone Generator 74 

7.4 Adjustable Multivibrator 75 

7.5 Flashing Light Circuit 76 

7.6 LED 1 -second Flasher 77 

7.7 Free -running Pulse Generator 78 

8.1 Basic dc Supply with Regulation 79 

8.2 Voltage Regulator 80 

8.4 Adjustable Voltage Regulator 81 

8.5 Voltage Regulator with Zen er Diode 82 

8.6 Voltage Regulator with Transistor 82 

8 





LIST OF WORKING CIRCUITS 




8.7 


Regulated Split Supply 


83 


9.1 


Electric Motor Speed Controller 


84 


9.2 


Electric Motor Speed Controller 


85 


10.2 


Low Pass Filter 


89 


10.2 


High Pass Filter 


89 


10.4 


Notch Filter 


90 


10.5 


High-Q_Notch Filter 


91 


11.6 


1-bit Memory' 


98 


11.7 


Flip-FIop Circuit 


98 


11.8 


J- K Flip -Flop 


98 


11.9 


D-type Flip-Flop 


99 


12.1 


Master Oscillator for Electronic Organ 


102 


12.2 


Basic Electronic Organ Circuit 


103 


12.3 


Sustain Circuit for Organ 


104 


12.4 
12.5 


Decay Control for Organ 


105 


Organ Percussion Circuit 


105 


13.1 


Hi-Fi Tone Control 


107 


13.3 


Simple Hi-Fi Tone Control 


109 


13,4 


Treble and Bass Tone Control 


110 


13.5 


Tone Control for Dual Supplies 


111 


13.6 


Automatic Brightness Control for LEDs 


112 


13.7 


LED Tuning Indicator 


113 


13.8 


Car Thief Alarm 


115 


13.10 


Ice Warning Indicator 


118 



13.11 Digital Voltmeter 

13.12 Infra-Red Transmitter 

13.13 Infra -Red Receiver 

13.14 Simpler Infra -Red Receiver 

13.15 Electronic Rev Counter 

13.16 Quartz Crystal Clock Circuit 

13.17 Alarm for Quartz Crystal Clock 

9 



120 
122 
123 
125 
126 
127 
127 



PREFACE 






INTEGRATED CIRCUITS (or ICs) are the building blocks from 
which modern electronic circuits are assembled. They save a 
lot of time in construction and give better performance than 
similar circuits built from separate components and, above 
all, are incredibly space saving. In these respects they are a big 
step ahead of single transistors and have made it easier for 
amateur constructors — as well as professionals— to build 
working circuits. 

There are thousands of different types of ICs, each of which 
may be adaptable to many different working circuits 
(although some of the more complex ones are designed with a 
limited range of application). This can be quite bewildering, 
especially knowing how and where to start. However, from the 
point of view of using ICs and putting them to work, there is 
no need at all to know the actual circuits they contain — merely 
what type of circuit they contain and how their leads or pins 
are connected to other components to complete a working cir- 
cuit. 

This is what this book is about. It explains and 'classifies' in- 
tegrated circuits in simple terms. It covers the various ways in 
which the simplest ICs — Op- Amps — can be worked; and 
describes a whole range of working circuits based on selec- 
ted and inexpensive — integrated circuits. The book con- 
tains a total of 84 different working circuits. 

In fact it is really a basic — and essentially practical — 
'course' on understanding and using integrated circuits. 



11 












Chapter One 

INTRODUCTION TO 
INTEGRATED CIRCUITS 

The transistor first appeared as a working device in 
1947, since which time it has been manufactured in hundreds 
of millions, It took a little time to realize that the same tech- 
niques used for producing individual transistors could be 
applied to complete circuits and sub-circuits containing both 
active components (e.g. diodes and transistors) and passive 
components (e.g. resistors and capacitors), with all necessary 
interconnections in a single unit familiarly known as a 'chip'. 

Apart from the obvious advantage of being able to produce 
complete circuits and sub-circuits in this way, the cost of pro- 
ducing a complex circuit by photo-etching techniques is little 
more than that of producing individual transistors, and the 
bulk of the circuit can be reduced substantially since trans- 
istors in integrated circuits do not need encapsulation or 
canning, and resistors and capacitors do not need 'bodies'. 
Another advantage is the potentially greater reliability offered 
by integrated circuits, since all components are fabricated 
simultaneously and there are no soldered joints. Also 
performance can be improved as more complex circuits can be 
used where advantageous at little or no extra cost. 

The next big step in integrated circuit construction was the 
development of microelectronic technology or extreme 
miniaturization of such components and integrated circuits. 
Photo-etching is readily suited to this, the main problem being 
in checking individual components for faults due to 
imperfections in the manufacturing process, and achieving a 
high yield of fault-free chips per 'wafer' manufactured. 
Rejection rates are liable to rise with increasing complexity of 
the circuit, but modern processes now achieve a very high yield. 

Basically an integrated circuit consists of a single chip of 
silicon, typically about 1.25 mm square (0.050 inches square) in 
size. Each chip may contain 50 or more separate components, 
all interconnected (although they may contain very many less 
for simpler circuits). The actual manufacturing process is 

13 



INTEGRATED CIRCUITS 

concerned with producing wafers, each of which may contain 
several hundred chips. These wafers are processed in batches, 
so one single batch production may be capable of producing 
several thousand integrated circuit chips simultaneously, 
involving a total of tens of thousands of components. 

It is this high production yield which is responsible for the 
relatively low price of integrated circuits — usually substantially 
less than the cost of the equivalent individual components in a 
chip produced separately, and in the case of some chips even 
less than that of a single transistor. The final selling price, 
however, is largely governed by demand. The integrated circuit 
is a mass -product! on item and the greater the demand for a 
particular chip, the lower the price at which it can be sold 
economically. 

Fig. 1 . 1 shows a typical and fairly simple IC produced as 



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1.1 Outline shape of a typical 8-pin dual-in-line integrated circuit, about 
1+ times actual size. 

a flat 'package' encapsulated in plastic. The drawing is approx- 
imately lj limes actual size (9.4mm long by 6mm wide). Fig. 
1.2 shows the complete circuit contained in this IC, comprising 
16 transistors, 8 diodes and 13 resistors. Fig. 1.3 shows the 
physical appearance of the chip, much magnified, when it is 
part of the wafer. The actual size of this chip is approximately 
2 . 5 mm by 2 mm . 

The actual component density or number of components per 
unit area, may vary considerably in integrated circuits. The 
figure of 50 components per chip has already been mentioned, 
which is typical of small-scale integration (SSI). It is possible to 
achieve much higher component densities. With medium-scale 
integration (MSI), component density is greater than 100 com- 
ponents per chip; and with large-scale integration (LSI), com- 
ponent density may be as high as 1000 or more components 
per chip. Both MSI and LSI are extensions of the original inte- 
grated circuit techniques using similar manufacturing 
methods. The only difference is in the matter of size and 

14 







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QFVSE1 MILL 



1.2 Schematic diagram of one half of a CA3240 BiMOS operational amp- 
lifier showing components and interconnections all iormed in the sub- 
strate of the chip. 

physical separation of the individual components and the 
method of inter-connection. 

Monolith ic a n d Hy b rid ICs 

Integrated circuits where all the components and 
connections are formed in the substrate of the 'chip' are known 
as monolithic ICs. There is a further class of ICs where the indi- 
vidual components (transistors, diodes, resistors, etc.), or even 
complete sub-circuits, are all attached to the same substrate 
but with interconnections formed by wire bonding. These are 
known as hybrid ICs. In hybrid circuits, electrical isolation is 
provided by the physical separation of the components. 

IC Components 

Transistors and diodes are formed directly on the surface of 
the chip with their size and geometry governing their electrical 

15 




T .5 Much enlarged illustration of the CA3240 chip containing two com- 
plete circuits like Fig. 1.2. Actual dimensions of this chip are 2,5 by 2 
millimetres. Grid dimensions marked around the outside of the 
diagram are in thousandths of an inch. 

characteristics as well as density level, etc. Where a number of 
such components are involved in a complete integrated circuit 
their performance is usually better than that of a circuit with 
discrete (separate) components because they are located close 
together and their electrical characteristics are closely 
matched. 

Resistors can be formed by silicon resistance stripes etched in 
the slice, or by using the bulk resistivity of one of the diffused 
areas. There are limits, however, to both the range and 
tolerance of resistance values which can be produced by these 
methods. 'Stripe' resistors are limited to a minimum width of 
about . 025 mm (0 . 00 1 in .) to achieve a tolerance of ] per cent . 
Practical values obtained from diffused resistors range from 
about 10 ohms to 30k ohms, depending on the method of 
diffusion with tolerances of plus or minus 10 per cent. Better 
performance can be achieved with thin -film resistors with 
resistance values ranging from 20 ohms to 50 k ohms. 

A method of getting round this problem when a high 

16 






INTRODUCTION TO INTEGRATED CIRCUITS 

resistance is required is to use a transistor biased almost to cut- 
off instead of a resistor in an integrated circuit where a 
resistance value of more than 50k ohms is required. This is 
quite economic in the case of integrated circuit manufacture 
and a method widely used in practice. 

Capacitors present more of a problem. Small values of 
capacitance can be produced by suitable geometric spacing 
between circuit elements and utilizing the stray capacitance 
generated between these elements. Where rather higher 
capacitance values are required, individual capacitors may be 
formed by a reversed -bias PN junction; or as thin -film 'plate' 
type using a tiny aluminium plate and a MOS (metal-oxide- 
semiconductor) second plate. The former method produces a 
polarized capacitor and the thin film method a non-polarized 
capacitor. The main limitation in either case is the relatively 
low limit to size and capacitance values which can be achieved 
'—typically 0.2pF per 0.025mm (0.001 in,) square for a 
junction capacitor and up to twice this figure with a thin film 
MOS capacitor, both with fairly wide tolerances (plus or minus 
20 per cent). Where anything more than moderate capacitor 
values are needed in an integrated circuit it is usually the 
practice to omit the capacitor from the circuit and connect a 
suitable discrete component externally. 

Both resistors and capacitors fabricated in ICs also suffer 
from high temperature coefficients (i.e. working values varying 
with temperature) and may also be sensitive to voltage 
variations in the circuit. 

Unlike printed circuits, it is not possible to fabricate 
inductors or transformers in integrated circuits at the present 
state-of-the-art. As far as possible, therefore, ICs are designed 
without the need for such components; or where this is not 
possible, a separate conventional component is connected 
externally to the integrated circuit. 

From the above it will be appreciated that integrated circuits 
are quite commonly used as 'building blocks' in a complete 
circuit, connected to other conventional components. A simple 
example is shown in Fig, 1 .4 using a ZN414 as a basic 'building 
block' in the construction of a miniature AM radio. Although a 
high gain device (typical power gain 72 dB) the integrated 
circuit needs a following stage of transistor amplification to 

17 



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1 .4 Complete radio circuit using a ZN414 integrated circuit connected to 
external components. 

Resistors 

Rl 100k ohms 

R2 1 kohm 

R3 100 k ohms 

R4- lOkohms 

R5- 100 k ohms 

Capacitors 

CI — tuning capacitor to match tuning coil 1.1 

C2-0.01nF 

CS-O.luF 

C4-0.1*4F 
LI proprietary medium wave aerial coil on ferrite rod; or 80 turns of 
30s. w.g. enamelled copper wire wound on ferrite rod (matching value 
of CI =250 pF). 

IC-ZN414 

TR - ZTX300 (or equivalent) 

Speaker — transistor radio crystal earpiece. 

power a crystal earpiece; high value decoupling capacitors; and a 
standard coil and tuning capacitor for the tuned circuit. The 
complete circuit is capable of providing an output of 500 milli- 
volts across the earpiece, with a supply voltage of 1,3 and 
typical current drain of 0.3 milliamps. 

1 .5 Examples of integrated circuit outlines. 

A 16-pin dual in-line 

B 14-pin dual in-line 

C flat (ceramic) package • 

D 3-lead transistor 'can' shape 

E 6-lead 'transistor' shape 

F S-tead 'transistor' "shape 

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INTEGRATED CIRCUITS 

The Shape o/ICs 

ICs come in various 'package' shapes. Quite a number have 
the same shape (and size) as a typical transistor and are only 
readily identified as an IC because of the greater number of 
leads emerging from the bottom (a transistor usually has only 
three leads). These shapes are defined by the standard coding 
adopted for transistor outlines, e.g. TO-5, TO-18, etc., which 
also identifies the individual pins by numbers (e.g. see Fig. 
1.5). 

Other ICs come in the form of flat packages with leads 
emerging from each side. These are three different arrange- 
ments used (sec also Fig. 1.5), 

1. Dual in-line, where the leads on each side are bent down 
to form two separate rows to plug directly into a printed 
circuit panel or IC holder. 

2. Quad in-line, like dual in-line, except that the leads on 
each side form two parallel rows. 

3. Flat, where the leads emerge straight and from each side 
of the package. 

In all cases leading numbering normally runs around the 
package, starting from top left and ending at top right (again 
see Fig. 1 .5). The number of leads may be anything from eight 
to sixteen or even more. 

Some types of holders designed to match standard pin con- 
figurations or flat shape ICs are shown in Fig. 1.6. These 
holders have similar pin configurations to the ICs they take. 
Their principal advantage is that they can be soldered to a 
printed circuit or Veroboard, etc., with no risk of heat damage 
to the IC itself since this is only plugged in after soldered con- 
nections are completed. Most circuit constructors, however, 
prefer to solder ICs directly to a printed circuit panel (or 
Veroboard). 






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1 .6 Examples of integrated circuit holders (Elect rovaluc). 



Chapter Two 

'GENERAL PURPOSE' ICs (ARRAYS) 

The description 'general purpose' is not accepted 
terminology but it is used here to describe integrated circuit 
chips which comprise a number of individual components, 
usually transistors and possibly also diodes, each component in 
the chip connecting to individual outlet leads. Thus by 
connecting to the appropriate three (or two) leads and 
individual transistor (or diode) it can be connected to an 
external circuit. Other chips of this type may also include 
components connected within the chip, e.g. transistors in 
Darlington pairs, but the same principle of application applies. 
The technical description of such a chip is an integrated circuit 
array. 

A simple example of such a chip is shown in Fig. 2.1. It con- 
sists of three transistors (two interconnected); two types of 
diodes; and a Zener diode. This particular chip is used in the 
voltage regulator circuit described in Chapter 8 (Fig. 8.4), 
using two of the transistors, the SCR diode and the Zener diode. 

This circuit design is shown in Fig. 2.2. The components to 
be utilized which are contained in the IC are enclosed in the 
dashed outline, i.e. TR1, TR2, D2 and DS. The other com- 
ponents in the chip (Dl and TR3) arc not required. Resistors 
Rl, R2, R3 and R4 and a capacitor C, are all discrete 
components connected externally. 

Fig. 2.3 re-examines the component disposition in the chip, 
together with the necessary external connections. Note that the 
arrangement of the leads or pin-out arrangement does not 
necessarily follow the schematic diagram (Fig. 2.1) where the 
pins are in random order to clarify connections to internal 
components. The actual pin-out arrangement on ICs follows a 
logical order reading around the chip. Schematic diagrams 
may or may not follow in the same order (usually not). 

Connections for completing the circuit of Fig. 2.3 are: 

Leads 1, 2 and 3 are ignored as Dl is not used. 

Lead 4 connects one side of the Zener diode to the common 

22 



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substrate 



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2.1 Schematic diagram of CA3097E integrated circuit array which con- 
tains two diodes, one zener diode, two NPN transistors and one PNP 
transistor. Numbered pin connections are also shown, these providing 
access to individual components in the chip. These pins are not in the 
physical order as found on the chip (see Fig. 2,3). 




D2 r- zener M 

* • diode 

--F-- j 1 



2.2 Voltage regulator circuit components within the dashed outline are in 
the CA3097E integrated circuit. Rl , R2, R3. R4 and Care external 
components. 



earth line and Lead 5 to Lead 13, connecting the Zener diode 
to the correct side of the SCR (diode). 

Leads 1 1 and 12 connect together (as the SCR is worked as a 
simple diode in this circuit and the gate connection is not 
required). 

Now to pick up the transistor connections. The base of TR1 

23 



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2.3 Completed voltage regulator circuit showing wiring connections made 
to the integrated circuit . Pins in this diagram are shown in the actual 
physical order they appear on the integrated circuit. For ease of 
reading , pins are shown numbered and enclosed in circles rather than 
numbered tags. On circuit drawings pin numbers may be shown cir- 
cled or not. 

Note. For clarity the integrated circuit is drawn much larger in 
proportion to the external components. 



(15) connects to the external resistor Rl ; and the collector lead 
(14) to the other side of Rl , which is also the input point for the 
circuit. The emitter lead (16) connects to output. 

TR2 and TRS in the chip are interconnected, but only one of 
these transistors is required. Connecting lead (6) to (9) shorts 
out TR2, which is not wanted. Connecting the emitter lead (8) 
of TR3 to 11-12 (already joined); the collector lead (9) to (6); 
and the base lead (7) to the centre tag of the external 
potentiometer R3 connects TR3 into the circuit. 

It only remains for the external component connections to be 
completed. These are: 

R2 to lead (14) and lead (12). 

Capacitor C to lead (6) and earth point. Lead (10) on the IC 
is also the substrate or earthing point of the IC, so should also 
be connected to the common earth line. 

One end of the potentiometer R3 to the top (output) line. 

The other end of the potentiometer R3 toR4. 

The other end of R4 to the bottom common earth line. 

24 



GENERAL PURPOSE ICs (ARRAYS) 

Spare Components 

A number of components in an array may not be used in a 
particular circuit, but the cost of the single IC can often be less 
than that of the equivalent transistors or diodes ordered 
separately and used individually to complete the same circuit. 
The circuit using the IC will also be more compact and 
generally easier to construct. 



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circuit 
CA 3600 



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2.4 Schematic diagram of CA3600 array (top) and voltage doubler circuit 
using TR2, TRS and TR4 from the array together with external com- 
ponents: 

R]=10kohms 

R2= Ikohm 

Cl = 2.5uF 

C2 = 2.5uF 

diodes Dl and D2 
The spare transistors in the array (TR1 and TR5) ran be used instead 
of separate diodes, connected for diode working by ignoring the 
collector leads. 



INTEGRATED CIRCUITS 

A little study sometimes shows where further savings are 
possible. Fig. 2.4, for example, shows a voltage doubier circuit 
for a 1 kHz square wave input signal, based on a CA3096E IC 
array which contains 5 transistors. Only three of these 
transistors are used in this particular circuit, leaving two 
'spare'. 

The circuit calls for two diodes Dl and D2 (as well as three 
resistors and two capacitors) to be added as discrete 
components. Transistors can also be worked as diodes (by 
neglecting the collector lead), and so the functions of Dl and 
D2 could be performed by the two 'spare' transistors in the 
array (thus using up all its components). 

Alternatively, since the current needs a square wave input 
signal, the two 'spare' transistors could be used in a 
multivibrator circuit to provide this input, and in this case 
using discrete components for Dl and D2. Since diodes are 
cheaper than transistors, this is a more economic way of using 
all the components in the original array. 



O * vo 




2,5 Astable multivibrator circuit using one third of CA3600E array. 
IC1-OTACAS080 
IC2-CA3600E 
Rl - 1 00k ohms 
R2 5k ohms 
R3 lOkohms 
R4-10kohms 
C-O.OluF 



T 



GENERAL PURPOSE ICs (ARRAYS) 

The fact that popular ICs are quite cheap means that it is 
seldom worth while going to elaborate methods of trying to use 
all the components available in an array, unless such utilization 
is fairly obvious, as above. Using only part of an array can still 
show savings over the purchase of individual components for 
many circuits. 

The astable multivibrator circuit shown in Fig. 2.5, for 
example, only uses one of the three complete switching circuits 
contained in the CAS600E array, associated with an OTA 
CA3080 integrated circuit and four external resistors. On the 
other hand, Fig. 2.6 shows a high gain amplifier circuit using 
all the components in the CA360QE array with external 
resistors. 

Constant Current Circuit 

A useful circuit employing the CA3018 integrated circuit 
array is shown in Fig. 2.7. This array comprises four transistors 
(two interconnected as a super-alpha pair) and four diodes. 



Input 




2.6 High-gain amplifier circuit using the complete CAS600E integrated 
circuit together with external components: 
Rl-lMohm 
R2-22Mohms 
R3-22Mohms 
CI-IjjF 
C2 luF 
C3 luF 



INTEGRATED CIRCUITS 



Tapping the super-alpha pair of transistors, a constant current 
source can be produced, the magnitude of this current being set 
by adjustment of the potentiometer Rl over a range of about 
0,2 mA to 14mA, depending on the actual supply voltage. 



R4 



-C 



CA 3018 



33 



7 



9 to 
18 volts 



M=>- C 



R1 



R2 



-O " ve 



2.7 Constant current circuit using components found in CA3018 array. 
External component values: 

R I 1 k o hms po te nt iometer 

R2- 470 ohms 

R3-3.Skohms 

R4 is the resistance of the load through which the constant 
current is to flow. 



tJ 



R1 



K 



CA 3018 



1 



^ 



R2 



output 

— O * ve 

I 

constant 

6 volts 

I 



p*ve 

I 

9 to 

10 volts 



4 O - VB 

2.8 Circuit giving a constant 6 volts output from a 9 to 18 volts supply 
voltage, again using the CA301 8 array. 
External Component values: 

Rl 3.3kohms. 

R2-4.7kohms 



GENERAL PURPOSE ICs (ARRAYS) 

The same integrated circuit can also be used as a constant 
voltage source— Fig. 2.8. In this case the constant voltage 
output is the Zener voltage of the transistor worked as a Zener 
diode, which is approximately 6 volts. 



29 



Chapter Three 
OP-AMPS 



OP AMPS 
Adder (Fig. 3.2) 

Input signals Vj , Vg . . V n are applied to the op-amp as shown 
through resistors Rl, R2 . . R n , The output signal is then a 
combination of these signals, i.e. giving the sum of the inputs. 



OP-AMPS (OPERATIONAL AMPLIFIERS) are a particular 
class of integrated circuit comprising a directly-coupled high- 
gain amplifier with overall response characteristics controlled 
by feedback. The op-amp gets its name from the fact that it can 
be made to perform numerous mathematical operations. An 
op -amp is the basic building block in analogue systems and is 
also known as a linear integrated circuit because of its response. 
It has an extremely high gain (theoretically approaching 
infinity), the actual value of which can be set by the feedback. 
Equally the introduction of capacitors or inductors in the 
feedback network can give gain varying with frequency and 
thus determine the operating condition of the whole integrated 
circuit. 



inverting 



output 








Z1 




12 






-| 






3 — r 


1 












1 


1 

V 
in 

1 






1 
\ 

1 


i 
t 




v i 

out 

1 



non- inverting 



3.1 A basic op-amp is a three-terminal device with the corresponding cir- 
cuit as shown. A triangular symbol is used to designate an op-amp. 



The basic op-amp is a three-terminal device with two inputs 
and one output — Fig, 3.1. The input terminals are described as 
"inverting' and 'non-inverting'. At the input there is a virtual 
'short circuit', although the feedback keeps the voltage across 
these points at zero so that no current flows across the 'short'. 
The simple circuit equivalent is also shown in Fig. 3.1, when 
the voltage gain is given by a ratio of the impedances Z2/Z1 . 

Some examples of the versatility of the op-amp are given in 
the following simple circuits: 

30 



' 




O v 



jJ practical circuit may need a resistor here 



3.2 Adder circuit based on an op-amp. This inverts the output. 



The specific performance of the op -amp as an adder can be 
calculated from: 



Ri 



Rn 



Note the minus sign. This means that the output is 'inverted', 
i.e. this circuit shows an inverting adder. 

By changing the inputs + to - , the op-amp will work as a 
non ■ inverting adder — Fig. 3 . 3 . 



practice! circuit may need a 
resistor here 




O v 



out 



3.3 Non-inverting adder circuit, i.e. the input and output have the same 
polarity of signal and are thus in phase. 



INTEGRATED CIRCUITS 



A mplifier or Buffer 

Fig. 3.4 shows the circuit for an inverted amplifier or 
inverter. The gain is equal to -R2/R1, i.e. if Rl = R2 the 




-O v 



out 



3.4 A circuit which inverts the input signal, known as an inverter. Voltage 
gainisR2/Rl. 

voltage gain is - 1 , meaning that the circuit works as a phase 
inverter. A suitable value For R3 can be calculated from: 



R3 = 



Rl x R2 
RlxR2 



To work as a non-inverting buffer (amplifier), the connec- 
tions are made as shown in Fig. 3.5. In this case the gain is given 
by: 

ga,n rT 




-O v 



out 



3.5 Non-inverting amplifier circuit where the gain is equal to 1 + R2/R1 . 

If the gain is unity, this is also known as a buffer. 



Multiplier 

This is the same circuit as Fig. 3.4, using precision resistors of 
the specified values for Rl and R2 to give an exactly constant 

32 






OP-AMPS 

gain (and thus multiplication of input voltage in the ratio 
R2/R1). Note that this circuit inverts the phase of the output. 

Adder /Subtracter 

Connections for an adder/ subtractor circuit are shown in 
Fig. 3.6. If Rl and R2 are the same value; and R3 and R4 are 
also made the same value as each other, then: 

Vout = V3 + V4-Vl-V2 




-O v 



3.6 Adder/sub tractor circuit. See text for calculation of component 
values. 



In other words, inputs to V3 and V4 give a summed output 
(V out = V3 + V4). Inputs VI and V2 subtract from the output 
voltage. 

Values for Rl , R2, and R3 and R4 are chosen to suit the op- 
amp characteristics. R5 should be the same value as R3 and 
R4; and R6 should be the same value as Rl and R2. 

Integrator 

Theoretically, at least, an op-amp will work as an integrator 
with the inverting input connected to the output via a 
capacitor. In practice a resistor needs to be paralleled across 
this capacitor to provide dc stability as shown in Fig. 3.7. 

This circuit integrates input signal with the following 
relationship applying: 

r JVindt 



Vout = 



Rl.C 
33 



'inO 




■o v 



out 



3.7 Op-amp integrator circuit. 



The value of R2 should be chosen to match the op-amp char- 
acteristics so that: 

R2 
Rl 



Voo = £t • V i( 



Differentiator 

The differentiator circuit has a capacitor in the input line 
connecting to the inverting input, and a resistor connecting this 
input to output. Again this circuit has practical limitations, so 
a better configuration is to parallel the resistor with a capacitor 
as shown in Fig. 3,8. 




-o v 



out 



3.8 Practical circuit for an op-amp differentiator. 



The performance of this circuit is given by: 

dVin 



Vout = - R2C1 



dt 



34 



OP-AMPS 

Differential A mplifier 

A basic circuit for a differential amplifier is shown in Fig. 
3.9. Component values are chosen so that Rl = R2 
and R3 = R4. Performance is then given by: 

Vout = Vin2-Vin 1 

provided the op -amp used can accept the fact that the 
impedance for input 1 and input 2 is different (impedance for 
input 1 = Rl ; and impedance for input 2 = Rl + R3). 



v In 1 O l=3 




-O v 



out 



3.9 Basic differential amplifier circuit. 



Log A mplifiers 

The basic circuit (Fig. 3.10) uses an NPN transistor in 
conjunction with an op amp to produce an output proportional 
to the log of the input: 

„ , , Vin 

Vout= - klogm^j- 

The right hand diagram shows the 'inverted' circuit, this 



f 




■O v. 



out 




r out 



3*10 Basic log amplifier circuit using a transistor in conjunction with an 
op-amp. 



INTEGRATED CIRCUITS 

time using a PNP transistor, to work as a basic anti-log 
amplifier. 

The capacitor required is usually of small value (e.g. 20pF). 

Log Multiplier 

Logarithmic working of an op-amp is extended in Fig. 3.11 
to give a log multiplier. Input X to one log amplifier gives log X 
output; and input Y to the second log amplifier gives log Y 
output. These are fed as inputs to a third op-amp to give an 
output fog XY. 

If this output is fed to an anti-log amplifier, the output is the 
inverted product of X and Y (i.e. X. Y). 




3.11 Thiscireuit pro vi des kigari thrnic working (see t ext ) . 



Voltage Follower 

Because of the inherent characteristics of an op-amp the 
connections shown in Fig. 3.12 will tie the two inputs together 
so that the output always follows the input, i.e. 

Vout = V in 

The value of such a voltage follower is that it offers high 
input resistance with low input current and very low output 
resistance. There are many practical applications of this type of 

36 



OP-AMPS 

circuit and a number of op- amps are designed specifically as 
voltage followers. 



> — 1 o 

n O +/ 



out 



3.12 Tying the two inputs of an op-amp together gives a voltage-follower 
circuit where V out = V in. A characteristic of this circuit is high input 
resistance and very low output resistance. 



Voltage-to-Current Converter 

The circuit configuration shown in Fig. 3.13 will result in the 
same current flowing through Rl and the load impedance R2, 



R2 



r 



R1 

-CZZr- 




-O v 



out 



3.13 Voltage-to-current convener using an op-amp. 

the value of this current being independent of the load and 

proportional to the signal voltage, although it will be of 
relatively low value because of the high input resistance 
presented by the non- inverting terminal. The value of this 
current is directly proportional to V in/ Rl . 

Current-to- Voltage Converter 

This configuration (Fig. 3.14) enables the input signal 
current to flow directly through the feedback resistor R2 when 
the output voltage is equal to Iin x R2. In other words, input 
current is converted into a proportional output voltage. No 
current flows through R2, the lower limit of current flow being 
established by the bias circuit generated at the inverting input. 

A capacitor may be added to this circuit, as shown in the 
diagram, to reduce 'noise'. 

37 




o v 



out 



3.14 Current -to -voltage converter using an op a tup. 

Current Source 

Use of an op-amp as a current source is shown in Fig. 3,15, 

— czn — 



V in O- 




out 



3.15 Circuit for using an op -amp as a current source. See text for com- 
ponent values required. 

Resistor values are selected as follows: 



R1 = R2 

R3 = R4 + R5 



Current output is given by: 



I out = 



R3.Vin 

Rl ,R5 



Multivibrator 

An op-amp can be made to work as a multivibrator. Two 
basic circuits are shown in Fig. 3.16. The one on the left is a free 

38 



Rl 




O v 



out 




—r 



3.16 Two basic circuits for a multivibrator, based on op-amps. Component 
values for the right hand circuit are: 

Rl-lMohm Cl-470pF 

R2 lOMohm potentiometer C2 0.1 pF 

R3-2kohm 

R4 — 1 kohm 

diode — silicon d i ode ' 

IC-CA741 



running (astable) multi -vibrator, the frequency of which is 
determined by: 

1 



f= 



2C.R1 log r 



2R3+1 
R2 



The right hand diagram shows a monostable multivibrator 
circuit which can be triggered by a square wave pulse input. 
Component values given are for a CA741 op-amp. 
See also separate chapter on 'Multivibrators.' 

Schmitt Trigger 

A Schmitt trigger is known technically as a regenerative com- 
parator. Its main use is to convert a slowly varying input voltage 
into an output signal at a precise value of input voltage. In 
other words it acts as a voltage 'trigger' with a 'backlash' 
feature, called hysteresis. 

The op -amp is a simple basis for a Schmitt trigger -see Fig. 
3.17. The triggering or trip voltage is determined by: 



Vtrip = 



V out . Rl 

R1 + R2 



39 



irt 




O v, 



out 



3.17 Schmitt trigger which gives an output once a precise value of varying 
input voltage is reached. An application of this circuit is a dc voltage 
level senser. 



The hysteresis of such a circuit is twice the trip voltage. 

Another Schmitt trigger circuit is shown in Fig. 3.18, the 
triggering point being approximately one-Fifth of the supply 
voltage, i.e. there is a 'triggered' output once the dc input 
reaches one-fifth the value of the supply voltage. The supply 
voltage can range from 6 to 15 volts, thus the trigger can be 



— o * ve 




supply 
voltage 
5-15 volts 



3.18 A more complicated Schmitt trigger circuit for general use. 
Component values: 
Rl-2.2k ohm 
R2-S.3k ohm 
RS- 3.3k ohm 
R4-470 ohms 
R5 — 5k ohm potentiometer 
RS SSkohms 
R7-22kohms 
IC-CA3018 

40 



OP-AMPS 

made to work at anything from 1 .2 to 3 volts, depending on the 
supply voltage used. The actual triggering point can also be 
adjusted by using different values for R4, if required. 

Once triggered, the output will be equal to that of the supply 
voltage. If output is connected to a filament bulb or LED (with 
ballast resistor in series), the bulb (or LED) will light once the 
input voltage has risen to the triggering voltage and thus 
indicate that this specific voltage level has been reached at the 
input. 

Capacitance Booster 

The circuit shown in Fig. 3.19 works as a multiplies for the 
capacitor CI, i.e. associated with a fixed value of CI it gives an 



original 
capacitor C 




f e - 



3.19 Capacitance multiplier circuit. The effective capacitance Ce is equal 
to the value or CI multiplied by R1/R2, 

effective capacitance Ce which can be many times greater. The 
actual multiplication ratio is R1/R2 so that making Rl ten 
times greater than R2, say, means that the effective cap- 
acitance of this circuit would be 10 x CI . 

As far as utilization of such a multiplier is concerned, the 
circuit now also contains resistance (R2) in series with the 
effective capacitance. 



Filters 

Op-amps are widely used as basic components in filter 
circuits. Two basic circuits are shown in Fig. 3.20. The one on 
the left is a low pass filter and the one on the right is a high pass 
filter. 
See also separate chapter on Filters. 

41 



INTEGRATED CIRCUITS 



oczw 




low- pass filter 

3.20 Two basic filler circuits using op-amps. 

Op-amp Parameters 

The ideal op-amp is perfectly balanced so that if fed with 
equal inputs, output is zero, i.e. 

V in 1 = V in 2 gives V out = 

In a practical op-amp the input is not perfectly balanced so 
that unequal bias currents flow through the input 
terminal . Thus an input offset voltage must be applied between 
the two input terminals to balance the amplifier output. 

The input bias current (I B ) is one half the sum of the separate 
currents entering the two input terminals when the output is 
balanced, i.e. V out = 0. It is usually a small value, e.g. a 
typical value is Ig = lOOnA. 

The input offset current (\ m ) is the difference between the 
separate currents entering the input terminals. Again it is 
usually of a very small order, e.g. a typical value is I,,, = lOnA. 

The input offset voltage (Vj ) is a voltage which must be 
applied across the input terminal, to balance the amplifier. 
Typical value, V; = lmV. 

Both Ij„ and Vu, are subject to change with temperature, this 
change being known as I;,, drift and V io drift, espectively. 

The Power Supply Rejection Ratio (PSRR) is the ratio of the 
change in input offset voltage to the corresponding change in 
one power supply voltage. Typically this is of the order of 
10-20uV/V 

Other parameters which may be quoted for op-amps are: 
Open-loop gain — usually designated Aj. 
Common-mode rejection ratio— designated CMPR or/K This is 

42 



OP-AMPS 

the ratio of the difference signal to the common-mode signal 
and represents a figure of merit for a differential amplifier. 
This ratio is expressed in decibels (dB). 

Slew rate — or the rate of change of amplifier output voltage 
under large — signal conditions. It is expressed in terms of 



43 



Chapter Four 

AUDIO AMPLIFIERS 

QUITE a NUMBER of linear ICs are designed as audio ampli- 
fiers for use in radio receivers, record players, etc. Again these 
are used with external components but physical layout, and the 
length of leads is relatively unimportant — unlike circuits 
carrying radio frequencies. The 'packaging' of such ICs can 
vary from cans (usually TO-5 to TO- 100 configuration) to 
dual-in-line and quad-in-line. In all cases they will usually have 
12 or 14 leads (but sometimes less). Not all these leads are nec- 
essarily used in a working circuit. They are there to provide 
access to different parts of the integrated circuit for different 
applications. Integrated circuits designed with higher power 
ratings may also incorporate a tab or tabs to be connected to a 
heat sink; or a copper slug on top of the package for a similar 
purpose. 

A single chip can contain one, two, three or more amplifier 



output 




Utilization of the first amplifier in CAS035 integrated circuit by 
tapping pins 1.2,8.9 and 10. This circuit gives a voltage gain of 100- 
160 with an input resistance of 50 k ohms and an output resistance of 
270 ohms. 
Component values: 

Rl-lOOkohms CI lOuF 

R2-100kohms . CS ljiF 

C3-10uF 



AUDIO AMPLIFIERS 

stages interconnected and following each other (technically 
referred to as being in cascade). Pin -out connections provide 
'tapping' points for using one or more stages separately or in 
cascade as required. 

The (RCA) CA3035 integrated circuit is just one example. It 
consists of three separate amplifier stages connected in cascade 
with a component count equivalent to 10 transistors, 1 diode 
and 15 resistors. Each amplifier stage has different character- 
istics. The first stage, which can be selected by connections to 
pins 1, 2, 3, 9 and 10 (see Fig. 4.1), is a wide band amplifier 
characterized by high input resistance (i.e. ideally suited to 
connecting to a preceding transistor stage). The working 
circuit using this stage is shown in Fig. 4. 1 . It has a gain of the 
order of 160 (44dB). 

The second amplifier in the CA3035 has a lower input resis- 
tance (2k ohm) and a low output resistance of 170 ohms. The 
gain is similar to the first stage (about 45dB). A working circuit 
with tapping points is shown in Fig. 4.2. 




4.2 Utilization of the second amplifier in CA30S5 integrated circuit by 
tapping pins 2,4.5,9 and 10. This circuit gives a voltage gain of 100- 
120 with an input resistance or 2 k ohms and an output resistance of 
170 ohms. 
Component values: 

Cl-lOuF 

C2-10uF 



The third amplifier is a wide band amplifier with a low input 
resistance (670 ohms) and a high output resistance (5k ohms). 
It offers a voltage gain of 100 (40dB). A working circuit is 
shown in Fig. 4.3. 

Amplifiers 1 and 2 can be cascaded; or amplifiers 2 and 3; or 

45 




R1 



st-il o 



output 

! i 



9 volts 
supply 

I 



4.3 Utilization of the third amplifier in CA3035 integrated circuit by 
tapping pins 6, 7. 8, 9 and 10. This circuit gives a voltage gain of 80- 
120 with an input resistance of 670 ohms and an output resistance of 5 
k ohms. 
Component values: 

Rl — Skohms 

CI- IOjmF 

C2-10jjF 

amplifiers 1, 2 and 3. Fig. 4.4 shows the external connections 
and components required to cascade amplifiers 1 and 2, 

Using all three amplifiers in cascade results in a gain of 
approximately 1 10 dB. The circuit in this case is shown in Fig. 

4.5. 




4.4 Circuit for using first and second amplifiers contained in CA3035 in 
cascade. This circuit gives a voltage gain of about 7000 with an input 
of 50 k ohms and an output resistance of 170 ohms. 
Component values: 

Rl -220kohms CI 10(iF 

R2 1.2kohms C2--0.22^F 

C3-0.04fjF 
C4 lOfiF 
C5 50(/F 



AUDIO AMPLIFIERS 

Modifying A mpHfier Performance 

The output impedance of an amplifier stage can be modified 
by connecting Rl to provide a negative feedback from output 
to input. This has the effect of reducing the working value of Rl 
and Rl/Av where Av is the amplifier open loop voltage gain. 
This is accomplished without affecting the actual voltage gain. 
In the case of cascaded amplifiers a capacitor C2 is needed in 
series with Rl to act as a block to dc (i.e. Rl only is needed for 
amplifier 1 part of CA 3035, CI being effective as a blocking 
capacitor in this case). Since amplifier 2 in this chip is directly 




12 volts 
supply 



O -ve 



4.5 This circuit shows all three amplifiers in CA3035 cascaded to give a 
voltage gain of about 200.000 
Component tallies; 

Rl-220kohms CI lOjiF 

R2-1.2kohms C2 0.04fjF 

R3-680ohms C3-0.22ptF 

R4-lkohm C4-0.05^F 

R5-4,7kohms C5-0.05^F 

C6-50(iI-' 
C7 10 ^F 

coupled to amplifier 1; and amplifier 2 is directly coupled to 
amplifier 3; the use of an impedance-matching resistor 
applied to amplifier 2 (or amplifier 3) will require the use of a 
blocking capacitor in series with the resistor. 

The gain of the amplifier stage can be modified by the use of 
a series resistor in the input (Rl). This acts as a potential 
divider in conjunction with the effective input resistance of the 

47 



INTEGRATED CIRCUITS 

stage so that only a proportion of the input signal is applied to 
the stage. In this case: 

Rl 

1 . actual voltage gain = R . + , 

2. input resistance = Ri + Rl/Av 
where Ri is the input resistance of the IC 

Thus by suitable choice of Rl and Ri, both voltage gain and 
input resistance of an amplifier circuit can be modified to 
match specific requirements. It follows that if a number of 
different resistors are used for Ri, the circuit can be given 
different response (sensitivity) for a given input applied to each 
value of Ri by switching. This mode of working is useful for pre- 
amplifiers. Virtually the same circuit is used for an audio 
mixer, separate input channels being connected by separate 
series resistors (Ri) and thence commonly connected to the 




4.6 Audio amplifier for radio receiver based on the TAA611 A55 
integrated circuit. Pin numbers shown are for the can-shaped version 
of this IC. 
Component values: 

Rl 22 k ohms 

R2-S0ohms 

Cl-5QuF/6voli 

C2-56pF 

CS-150pF 

Gt-lfff 

C5-500*iF/12volt 

C6-100pF/12volt ■ 

loudspeaker — 8 ohms 






AUDIO AMPLIFIERS 

input. In this case each channel has the same input resistance 
with an overall gain of unity. 

Fig. 4.6 shows a circuit for a low power (1.8 watt) audio 
amplifier using a TA 611 monolithic integrated circuit. This 
particular IC is available in two configurations, a TO- 100 
metal case and in a quad -in-line plastic package. Lead 
positions are shown in Fig. 4.7 for the two different config- 
urations. 

This is a particularly attractive circuit for it needs a 
minimum number of external components and is capable of 



T 

7mm 

T 

8mm 



7 6 5 4 3 2 1 

nnnnnnn 



TAA611 A 12 



1 



uuuuuuu 

B 9 10 11 12 13 14 




Mm 



TAA611 
AS5 




T 

6m in 

Jl 



4.7 The two versions of the TAA61 1 integrated circuit. The TAA61 1 A55 
is a 14-pin dual-inline package. The TAA61 1 A55 is a 'can* shape 
package in a metal case (TO- 100). The circuits are identical so either 
can be used in Fig. 4.1 with the same external components. Note, 
however, the different pin-out arrangement for the TAA611 AI2 on 
the left. 

driving an 8-ohm loudspeaker direct with any supply voltage 
between 6 volts and 12 volts. Also it does not require a heat 
sink. 

Exactly the same circuit can be used with a number of other 
integrated circuits in the same family, offering higher output 
powers. These are the TA611B and TA611C. The only 

49 



INTEGRATED CIRCUITS 



TA611C 

supply volts 6 - 1 8 

3.3 watts 

220k ohms 

150 ohms 

25yF 

82pF 

1.2uT 

omit 

500uF 

lOOuF 



difference is the values required for the external components 
required, viz: 

TA611B 
supply volts 6-15 
max. power output 2.1 watts 

Rl 22k ohms 

R2 30 ohms 

CI 50wF 

C2 56pF 

C3 150pF 

C4 omit 

C5 SOO^F 

C6 IOOmF 

Lead arrangement for theTA61IB and TA61IC are the same 
asTAASll A12. 

Because of its higher power the current based on the TA61 1C 
really requires the IC to be mounted with a heat sink (Chapter 5 
deals specifically with heat sinks), although this is not absol- 
utely essential. The type is, in fact, available with a special 
mounting bar or spacer to which a heat sink can be attached. 
The recommended method of mounting is shown in Fig, 4.8, 
the heat sink itself being a piece of aluminium sheet cut to a 
suitable size and bent to the shape shown. The IC itself has a 
copper slug on its top face on to which the heat sink sits (and is 
clamped down by the mounting bolts). Better thermal contact 
between the IC and the heat sink can be achieved if the contact 
area is very lightly coated with silicon grease. 

There are other methods of fitting heat sinks to this IC (and 
other types). The TA611C is also available with an external 
bar, the ends of which can be soldered to copper 'patches' on 
the printed circuit panel (also shown in Fig. 4.8). In this 
example the copper areas form the actual heat sink. A suitable 
area in this case would be about 30 mm square for each copper 
patch. These copper areas are, of course, merely used for heat 
dissipation and are not part of the actual printed circuit as 
such, although it is normally advisable — and necessary with 
some types of IC — to connect the heat sink area to the common 
earth of the circuit. It is just a convenient method of making 
heat sinks integral with (and at the same time as) the printed 
circuit panel. 

50 





!14S_ .254 .! _2 

823 T 15.24* 
31.70 



25 4 



1 3MHIHMH1 



:V ° . f ' $ 



4.8 Aluminium sheet heat sink applied to the TA61 IC integrated circuit 
{(eft) and alternative external bar fitted to this IC (right) for connect- 
ing to heat sink areas on copper of printed circuit board. 



A further audio amplifier based on a TBA641B integrated 
circuit is shown in Fig, 4.9. This is a little more complicated in 
terms of the number of external components used but has the 
advantage of driving a 4-ohm speaker (the more readily 
available value with larger loudspeakers) and is suitable for 
direct coupling of the input. It will operate on a supply voltage 
ranging from 6 volts to 16 volts and give 4.5 watts output power 
at 14 volts. Again the IC needs mounting with a heat sink of the 
type illustrated in Fig. 4.8. 

Short Circuit Protection 

A feature of many audio amplifier circuits is thai if the 
output is shorted when the circuit is switched on (e.g. loud- 
speaker connections accidentally shorted), excessive current 
may be passed by the output transistors sufficient to destroy 

51 






IN( 



lOkD 




4.9 Audio amplifier for 4 -ohms loudspeaker based on the TBA641 B inte- 
grated circuit. Component values are shown on the diagram (SGS- 
Gates). 



them. It is possible to provide short-circuit protection with 
additional circuitry limiting the current which can flow 
through the output transistors. This can readily be incor- 
porated in an IC, an example being the TCA940 designed as a 
10 watt class B amplifier. Other characteristics of this partic- 
ular IC are high output current (up to 3 amps) very low 
harmonic and crossover distortion and a thermal shut down 
feature (See later). 

The circuit is shown in Fig. 4.10. Supply voltage is up to 24 

volts. Power rating depends both on the supply voltage used 

and the resistance of the loudspeaker: 

Supply voltage 4-ohm speaker 

20 10 watts 

18 9 watts 

16 7 watts 

A feature of this circuit is that the bandwidth is controlled by 
the values of Rf and CS and C7. For a value of Rf = 56 ohms 
with C3 = lOOOpF and C7 = 5000pf the bandwidth is 20kHz. 
For the same capacitor values the bandwidth can be reduced to 
10 kHz by making Rf ■ 20 ohms. For the original resistor value 
(Rf = 56 ohms), the bandwidth can be reduced to 10kHz by 
making C3 = 2 OOOpf and C7 = 1 OOOpF. 



8 -ohm speaker 
6.5 watts 
5 watts 



52 



Input 




l — B^?_ tca9 *° 



JL C2 C3 R " 



-O-vo 



4,10 10-watt amplifier circuit based on the TCA940 integrated circuit. 
The TCA940 is a 12-lead quad-in-line plastic package. 
Component values: 

Rl-lOOkohms 

R2-56ohms 

RS-lOOohms 

R4-lohm 

Cl-100|iF/3volt 

C2-100|wF/15voh 

C3-4700pF 

C4-lu:F 

C5-1000pF 

C6-100piF/15volts 

C7 — 100piF/25 volts 

C8-0.1(iF 

C9-200Q>F/ 16 volts 

Circuit assembly is straightforward, except that the IC needs 
a heat sink. It is provided with tabs which should be bolted to 
an external aluminium sheet heat sink of generous area. 

Thermal Shut Dottm 

The short-circuit protection built into this IC effectively 
works as a power-limiting device. It is only effective on a short- 
duration basis, i.e. to provide protection against temporary 
overload and short circuiting of the output. An additional 
circuit is included to ensure that regardless of how long a short 
circuit is present across the output the junction temperature of 
the output transistors is kept within safe limits. 

53 



INTEGRATED CIRCUITS 

In other words, this additional piece of circuitry incor- 
porated in the IC provides complete protection against a 
shorted output. It also has another advantage. The same 
protection is present if there is another cause of overheating, 
e.g. the heat sink used is not really large enough for the job it is 
intended to do. The thermal shut-down circuitry simply reacts 
to the junction temperature becoming too high by reducing the 
output current and power to compensate. 

Hi- Fi St ereo A mpHfier 

The excellent performance and extremely good stability 
possible with integrated circuits makes them a logical choice 
for Hi-Fi circuits. The TDA 2020 monolithic integrated 
operational amplifier is an excellent up-to-date exampleof such 
a device, designed to be used as a Class B audio power amplifier 
for Hi-Fi circuits. It is capable of providing a 20-watt power 
output into a 4-ohm loudspeaker with a supply voltage of 18 
volts, and with a guaranteed output power of 15 watts. It is also 
a device for providing high output current (up to 3.5 amps) and 
has a very low harmonic and cross-over distortion. It also incor- 
porates short-circuit protection and thermal shut-down 
protection. 

The TDA2020 is in the form of a quad-in-line plastic 
package of conventional appearance with 14 leads. Because of 
its high power rating it is intended to be used with a specially 
formed heat sink mounted on a spacer designed to provide 
proper thermal contact between the IC itself and the heatsink 
when assembled on two bolts — Fig. 4.11. The most negative 
supply voltage of the circuit is connected to the copper slug on 
the IC and hence also to the heat sink. 

The basic amplifier circuit is completed by the addition of 
four external resistors and seven capacitors, plus a coupling 
capacitor to enable the circuit to be used with a split power 
supply. This provides direct drive for a 4 ohm loudspeaker. 
Since the Hi-Fi circuits are usually stereo, two ICs are used in 
this basic circuit configuration, each IC powering its own loud- 
speaker. The complete circuit is shown in Fig. 4.12. 

Another simpler stereo audio amplifier circuit is shown in 
Fig. 4.13, based on the (Mullard) TDA1009 integrated circuit. 
This IC is a low frequency Class B amplifier with no crossover 

54 







Htfllimh 

",„ ■ IWS'CJW 



till, tort giwtl 



f 



E 



l l l I t l i.| " 



HZ. 



— M m*<4 



ur 7 — u=j 

4.11 Heat sink for TDA20S0 integrated circuit. 



INTEGRATED CIRCUITS 
distortion designed for use with a minimum number of 
external components. It delivers 2x6 watts output power at 10 
per cent distortion into speakers of 4-ohms impedance with 8 to 
16 volts supply; and can also deliver the same power into 
speakers with 8-ohms impedance using a 24 -volt supply. The IC 




loudspeaker 



O ' ve 

split supply 

O -ve 



loudspeaker 



4.12 Stereo amplifier circuit with split supply voltage 
Component values: 
Rl- lkohm 
R2- 100 k ohms 
R3 — I ohm 
R4- lOOkohms 
R5- 47 k ohms 
R6 lkohm 
R7- lOOkohms 
R8-lohm 
R9-100kohms 
IC1 -TDA2020 
IC2 TDA2020 
loudspeakers — 4 ohms 



jge± 


17 to ±24 volts 


CI 


-O.ljiF 


C2 


-6.1p7 


cs 


68 pF 


C4 


-0.1 pf 


C5 


-O.l^F 


C6 


-47juK 


C7 


-lOOuT 


C8 


100|uF 


C9 


- 47^F 


CIO 


-Q.l^F 


Cll 


B8pF 


C12 


-0,1 mF 



AUDIO AMPLIFIERS 

incorporates short circuit protection for supply voltages up to 
16 volts and also thermal protection. Input impedance is 45k 
ohms. 

The addition of capacitors C9 and CIO (shown dotted) 
provides 'bootstrapping'. This provides increased output 
power. 

High Power A mplifiers 

Most of the original IC audio amplifiers which appeared on 
the market had a relatively limited power output and thus 



Q +vb suppfy voltage 



C1 ; 

o- 



V_J " r-IK 



..T^T 




C12 



R8 



Q -ve supply voitage 



4.13 Bridge amplifier circuit with split power supply ±17 volts to ±22 



volts. 




Component values: 




Rl-lOOkohms 


CI -100,1/F 


R2-33kohms 


C2 -0.1 uF 


R3- 100 k ohms 


C3 -68pF 


R4 — 4 ohms 


C4 -0.1 uE 


R5— lohm 


CS -4.7uF 


R6 lOOkohms 


C6 -100^F 


R7- 100 k ohms 


C7 -O.luF 


R8- lOOkohms 


C8 -O.luF 




C9 -560pF 


IC1 TDA2020 


ClO-O.l^F 


IC2-TDA2020 


Cll-0.1fiF 


loudspeaker — 4 or 8ohms 


C12-0.1^F 



57 



INTEGRATED CIRCUITS 



needed to be associated with a further stage or stages of 
transistor amplification to give more than a few watts output. 
Single IC amplifier chips are now readily available with output 







-O *"e 



right 
channel 



O-vo 



4.14 Simple 2x6 watts stereo amplifier circuit using a minimum of 
external components (Mullard). 

Note the rectangular symbol used For the IC. This is often more con- 
venient than a triangle or separate triangles when the integrated 
circuit has a large number of pins. 
Component va lues: 

Resistors 

Rl -4,7 ohms 

R2 -4.7ohms 

Capacitors 



CI 


lOOmF 


C2 
C3 
C4 


330 pF 
-330pF 
-lOOmF 


C5 


- 100 mF 


C6 


lOOmF 


C7 
C8 
C9 " 
CIO' 


lOOOuF 
-lOOO^F 
-47/iF 

47uF 


'bootstrap capacitors 
hum filter 47^F 
IC--TDA1009 



58 



AUDIO AMPLIFIERS 
powers from 1 to 5 watts and substantially higher outputs are 
obtainable from later developments capable of handling even 
higher voltages and currents with satisfactory thermal stability. 

Bridge Amplifiers 

Even higher outputs are obtainable from bridge amplifier 
circuits. These can be used to increase power from output for a 
given supply voltage, or maintain a high power output with a 
reduced supply voltage. Bridge connection can give four times 
the output power under a given load with the same supply 
voltage; or twice the output power at a fixed peak current if the 
load impedance is doubled (e.g. using 8-ohm loudspeaker(s) 
instead of 4-ohm loudspeaker (s)). 

An example of this type of circuitry, again using the 
TDA2020 integrated circuit is shown in Fig. 4.14. It is capable 
of delivering 30 watts power output in an 8-ohm loudspeaker 
with a supply voltage of ± 17 volts. 



59 



Chapter Five 

HEAT SINKS 

WHERE INTEGRATED CIRCUITS handle moderate powers 
and a heat sink is necessary to dissipate heat generated within 
the IC itself, areas etched on the copper of a printed circuit 
board can conveniently be used as heat sinks. ICs which are 
suitable for heat sinks of this type are usually fitted with a tab or 
tabs for soldering directly to the copper bands forming the heat 
sink. 

The area of copper needed for a heat sink can be calculated 
quite simply, knowing the relevant circuit parameters. First it is 
necessary to determine the maximum power to be dissipated, 
using the formula: 



Power (watts) = 0.4 „=* + V 3 . Id 



where V s is the maximum supply voltage 

Id is the quiescent drain current in amps under 

the most adverse conditions. 
Rl is the load resistance (e.g. the loudspeaker 

resistance in the case of an audio amplifier 

circuit). 

Strictly speaking the value of V, used should be the battery 
voltage plus an additional 10 per cent, e.g. if the circuit is 
powered by a 12-volt battery, the value of V s to use in the 
formula is 12 + 1 .2 = 1 3.2 volts. This allows for possible fluctu- 
ations in power level, such as when using a new battery. If the 
circuit has a stabilized power supply, then V, can be taken as 
this supply voltage. 

The quiescent drain current (Id) is found from the IC par- 
ameters as specified by the manufacturers and will be 
dependent on supply voltage. Figures may be quoted for 
'typical' and 'maximum'. In this case, use the maximum values. 

Fig. 5.1 then gives the relationship between power to be dis- 

60 



HEAT SINKS 

sipated and copper area, based on a maximum ambient 
temperature of 55°C (which is a safe limit for most IC devices). 
Example: Supply voltage for a particular IC is 12 volts. Load 
resistance is 4 ohms and the maximum quiescent current drain 
quoted for the IC at this operating voltage is 20 milliamps. The 
supply voltage is not stabilized, so the value to use for V s is 

12+ 1.2= 13. 2 volts 



13 2 3 
Thus power = 0.4 x- — — 



(13.2x0.020) 



= 2.178 + 0.264 

= 2.422 watts (say 2.5 watts) 



From Fig. 5.1, a suitable copper area is seen to be a 40mm 
square. 



length of sou ore area * inches 
0.5 1 1.5 



1 I I I 




i i. 


r~ 


i 


i_i. : i 


i i i i 


■— r-r r t 


















































* * 
















/ 
/ 
















i_ 
















i 

















10 



50 



BO 



20 30 40 

length of square area - millimetres 
5.1 This graph can be used to determine the size of squares of copper 
required for heat sinks on printed circuit boards. Size is given as 
length of a square. Any other shape of the same area can be used (see 
text ). 



INTEGRATED CIRCUITS 

This heat sink area can be arranged in two squares (if the IC 
has two tags); or a single square (if the IC has one tag) — Fig. 
5.2. Of course, the area does not have to be a square. This is 
simply the easiest shape to calculate. It can be rectangular, 
regular or irregular in shape, provided there is sufficient area. 
A point to be borne in mind, however, is that with any shape 
the copper area nearest the tag will have greater efficiency as a 
heat dissipator, so shapes which concentrate the area in this 
region are better than those that do not. If such a shape cannot 



square areas of copper 




hH 



tab 



t \n \y/\ 



10 



tabs 



h'-i i — -- i 



5.2 Copper area determined from Fig. 5.1 is Tor two equal squares (one at 
each end of the IC). If a single square is used at one end of the IC, its 
area needs to be slightly greater for the same heat dissipation. 

be incorporated conveniently on the printed circuit layout a less 
efficient shape has to be used, then it may be necessary to 
increase the actual area of copper to compensate. Copper areas 
given in Fig. 5.1 should be adequate since most ICs can be 
worked at fairly ambient temperatures without trouble (e.g. up 
to 70°C). Very approximately this higher temperature oper- 
ation will be provided by a copper area of a little more than one 
half that given by the graph, so there is a fair margin for error 
available when using this graph. 

The graph also shows that the area of copper necessary to 
dissipate powers of 3 watts or more tends to become excessive, 
compared with the area of printed circuit panel actually re- 
quired for the circuit itself . Where higher powers have to be dissi- 
pated, therefore, it is usually more convenient (and more 
efficient) to dissipate heat by an external heat sink fitted to the 
IC itself. Some examples of external heat sinks are shown in 
Figs. 4.8,4.11 and 5.3. 



62 





good shape poor strode - needs more area 

5,3 Good and poor shapes for heat sink areas on PCBs. 



<^1 




5.4 Examples of external heat sinks for fitting to power transistors and 
integrated circuits (see also Figs. 4.8 and 4.11). 



Chapter Six 

COMPLETE RADIO CIRCUITS 

THE DEVELOPMENT OF RADIO CIRCUITS around a single 
IC with the same physical size (and shape) as a single transistor 
is exemplified by the following. The IC is the Ferranti ZN414 
which contains the equivalent of 10 transistors in a complete 
TRF (tuned radio frequency) circuit providing three stages of 
RF application, a detector and age (automatic gain control). 

The ZN414 has three leads, identified as input, output and 
ground. It provides a complete radio circuit in itself to be 
connected to an external tuned circuit, an output decoupling 
capacitor, a feedback resistor and second decoupling 
capacitor, and an AGC resistor. As with any high gain RF 
device, certain requirements should be observed to ensure 
stable and reliable operation. These are: 

1 . All leads connecting components to the ICs should be kept 
as short as possible . 

2. The output decoupling capacitor should be connected 
with very short leads to the output and ground leads of the 
ZN414. 

3. The tuned circuit should be kept as far away as possible 
from the battery and from the loudspeaker and leads 
connecting these components to the circuit. 

4. The 'earthy' side of the tuning capacitor (the moving part) 
must be connected to the junction of the feedback resistor 
and the second decoupling capacitor. A basic radio 
circuit using a minimum of components is shown in Fig. 
6.1. 

A basic radio circuit using a minimum of components is 
shown in Fig. 6.1, LI and CI is a conventional tuned circuit. 
e.g. a high-Q. proprietary coil on a ferrite rod with a matching 
value of tuning capacitor. Alternatively, LI can be made by 
winding approximately 80 turns of 0.3 mm diameter (30 swg) 
enamelled copper wire on a ferrite rod 4cm (Hin) to 7.5cm 
(3in)long. In this case a matching value of CI is 150pF. 

This circuit will provide sufficient output power for driving a 

64 



* 



C1 



■CZJ- 

R1 



— o ,ve 



input 



C2 




crystal 


I 


earoiece 


>, 


(low 


91 


I nwedBnce ) 


O 



output 



ground 



-o - ve 



6.1 The ZN414 integrated circuit consists of a preamplifier followed by 
three stages of rf amplification and finally a transistor detector. It is a 
'complete" radio circuit requiring a minimum of external components 
to work. These are: 

LI and CI — ferrite rod aerial coil and matching tuning capacitor 

Rl lOOkohms 

C2 -O.OluT 

CS-O.lpF 
Sensitive (low impedance) crystal earpiece (500 ohms) or less. 

ZN414 lead identification 



input 



output 




*' . ,| J crystal | 

J- earpiece 



■*"♦ 



-Q -"• 



6.2 To deliver enough power to work a high impedance crystal earpiece 
the ZN414 is used in conjunction with an additional stage of transistor 
amplification. It delivers 600 mW peak output. This is the same 
circuit as Fig. 1.4 (Chapter I) with the addition of a volume control 
(R6) 
Component mktt& 

Rl- lOOkohms LI & CI as Fig. 6.1 

R2 lkohm C2--0.01uT 

RS - lOOkohms C3-0.1|jF 

R4 lOkohms C4-0.1f4F 

R5-100ohrm 

R6 25 Oo rims potentiometer 



INTEGRATED CIRCUITS 

sensitive low impedance earpiece with an equivalent resistance 
of approximately 500 ohms. To work a high impedance crystal 
earpiece an additional stage of amplification is needed. This 
modified circuit is shown in Fig. 6.2, requiring four more 
resistors, a potentiometer, another capacitor and a ZTX300 
transistor (or equivalent). The potentiometer R4 and resistor 
R5 provide volume control (by adjustment of R4). This can be 
omitted if the receiver is to be brought down to minimum size, 
as the directional effects of the ferrite rod aerial will normally 
provide all the volume control necessary. In that case, replace 
R4 and R5 with a single 270-ohm resistor. 

Fig. 6.3 shows the circuit extended to give a performance 
comparable to that of most domestic portable transistor 
receivers, driving an 8-ohm loudspeaker and formed by a 9-volt 
battery. This circuit does use six additional transistors and a 
number of other components, but the component count (and 
cost) is still substantially less than that of an all -transistor 
receiver of comparable quality (it is the equivalent of a 16 tran- 
sistor set). 

AM/ FM Radio 

A design for a high performance AM/FM radio receiver is 
shown in Figs. 6.4 and 6.5. These circuits are by Mullard and 
are based on their TDA 1071 integrated circuit which 
incorporates an AM oscillator, an AM mixer with age, a four- 
stage differential amplifier and limiter and a four-quadrant 
multiplier. Both AM and FM functions are combined in the 
multiplier, giving symmetrical demodulation on AM and 
quadrative detection with squelch on FM, 

Fig. 6.4 shows the AM circuit, working from a ferrite rod 
aerial. Fig, 6.5 shows the circuit for the additional front-end 
required for FM working, connected to an FM aerial. These 
circuits will work on any battery voltage from 4.5 volts to 9 
volts. For FM operation, the AM-FM switch (SW4) moved to 
the FM position switches off the AM mixer and oscillator and 
brings the FM front -end circuit into operation. The squelch 
circuit is separately controlled by SW1 , the threshold of squelch 
operation being set by the potentiometer Rll in Fig. 6.4. 

Component values are given on the two circuit diagrams. A 
complete list is also given on pages 70 and 71 . 

66 




■a I 



- e 
■3 e 

-a a p 

£ So— 

IJ Jl > 

* 8 a. 

? 2. 3 



■5 1.2 

c 

o g."S 
-a E a 
% .o .<2 
.S U £* 
« -a S 

3 1 « 



- £ 5 

1> > 

■« ■* b 

a* -a 
AM - 

■= •£ H 
< h -C 

en 




6.4 Circuit diagram of AM/FM receiver using the TDA1071 integrated 
circuit (Mullard) 



6.5 Front -end circuit for FM operation of the receiver given in Fig. 6.4 
(Mullard) 






1 



>- Si' 



Hh 



ES 



c 

aijS 
B - 



a 

-1=)- 






I 
I 

fl 



1 







ti a 




HI- 








- i 1 - 

Hh 

c 












"N 



X 



_ rv^4w^ 












5 






turn, 0.071mm enamelled 



Former: Toko 7 P 0092 



Components: AM/FM receiver circuit 

Resistors Winding data 

All resistors CR25 10% T l Primary: 12 turns, 0.071mm 

unless stated A j 

Rl ^fiOkQ enamelled copper 

^ 220kO Secondary: 2 turns, tapped at 1 

R3 220ktt 
R4 8.2kfi 

^ ^l?^ 1 T2 Primary: 12 turns, tapped at 1 

„5 .,-" turn, 0.071 mm enamelled 

R8 15kfl C ° Pper 

„ q ,_q Secondary: 3 turns, 0.071mm 

R10 lOOkO T; namd, T n T P ?PnaQ9 

mi M in,r • . l'ormfr: Ioko/P0092 

Rll 22k£l Miniature carbon T3 Pri : 3 turns n. 71mm 

preset potentiometer, ,/ , 

Philips 2322 410 03309 enamelled copper 

R19 fiSQ Secondary: 120 turns, tapped at 

„,„ „ „q 5 turns, wound over primary, 

£j^ 33 ^ 0.071 mm enamelled copper 

Capacitors 

CI 68pF 

C2 lOOnF 

copper 

Secondary: 86 turns, wound 

over primary, 0.071mm 

enamelled copper 

Former: Toko 0089 

T5:M.W.- 



FormcT:Toko7P0089 

T4 Primary: 9 turns, tapped at 5 

turns, 0,071mm enamelled 



C3 27pF 

C4 68pF 

N5 68nF 

C6 lOOnF 

C7 68nF 



C8 270pF 

C9 120pF 

C10 lOOnF 

Cll 560pF 

CI 2 22pF 

CI 3 270pF* 

CI 4 130pF* 

C15 22pF 

CI 6 22nF 

C17 100uF,4V 

CI 8 68nF 

C19 lOOnF 

C20 68nF 

C21 10uF,25V 

C22 3.3nF 

C23 230nF 

C24 22nF 

C25 150pF 

C26 !8pF 

C27 3.3pF 



Primary: 78 turns, wound in a 
single layer, 3 x 3 x 3 x 
0.063mm lit* 

Secondary: 4 turns, wound over 
the earthy end of the primary 
3x 3x3x0. 063 mmlitz 
L.W.- 

Primary: 210 turns, wave- 
wound, 9 x 0.063mm litz 
Secondary: 12 turns, wound 
under the primary, 9 x 
0.063mm litz 

For T5 the coils are mounted 

on a ferritc rod, 178mm in 

length, diameter 9.5 mm. 

LI 8 turns, 0.071mm enamelled 

copper. Former: Toko 7P 0092 

Switch 

SW1 to SW4 4- pole 2- way switch 



*These components form part Integrated circuit 
of the ganged tuning capacitor IC1 TDA 1 07 1 



Components: FM front-end circuit 



Resistors 

All resistors CR25 10% 

Rl 1.2k« 

R2 12kfi 

R3 27kfi 

R4 27kfi 

R5 12kfi 

R6 Ikfi 

R7 39fl 

R8 27kf2 

R9 12kfl 

R10 100S2 

rii ion 

R 1- 

2 lkfl 
R 1- 

3 39fi 



Capacitors 

CI 18pF 

C2 3.3nF 

CS 4.7pF 

C4 3,3nF 

C5 12pF* 

C6 18pF 

C7 3.3nF 

C8 18pF 

C9 12pF* 

C103.3nF 

C112.7pF 

C125.6pF 

C133.3nF 

C14 56pF 

C!53.3nF 

C1622nF 

Winding data *]\ e * e components form part 

Tl Primary: 2 turns, 0.031mm °* the ganged tuning capacitor 
enamelled copper 
Secondary: 2 turns, 0.031mm 
enamelled copper 
Former: Ncosid 5 mm with 
ferrite core 
T2 Primary: 4 turns, spaced one 
diameter 0.71mm enamelled 
copper 

Secondary: 1 turn, interwound 
with the primary 0.71mm 
enamelled copper 
Former: Neosid 5 mm with 
ferrite core 
LI 3 turns, spaced one diameter Transistors 

and tapped at ljturns. TR1,TR2,TR3 BF195 

0.71 mm enamelled copper 

Former: Neosid 5mm with Diode 

ferritecore Dl BB110 

Printed Circuit Layout 

Fig. 6.6 shows a printed circuit layout for the complete 
circuits of Figs. 6,4 and 6.5, using the components specified 
above. Components with the subscript F are those in the front 
end circuit (Fig. 6.5). One additional component is also 
shown — a 300pF capacitor adjacent to the medium wave/long 
wave AM aerial switch, which does not appear on the relevant 
circuit diagram (Fig. 6.4). 

71 



of! 







— ^ i - 1 , \u. t, u-r^^M Vr 




Wh 










Hi? 



iS ml 



PI 

6.6 Printed circuit layout and component positions for constructing the 
circuits of Fig. 6.4 and 6.5. (Multard) 

Note also that this circuit is complete only up to the audio 
out put stage — i.e. it needs to be followed by an audio amplifier 
and speaker(s) — see Chapter 4 for possible circuits to use. 

72 



Chapter Seven 
MULTIVIBRATORS 



THE SIMPLEST FORM of IC multivibrator merely uses an op- 
amp in a basic oscillator circuit such as that shown in Fig. 7.1 . 

R3 

-T 



in Q. 




■O out 



JLTLil 



7.1 Simple multivibrator (or square wave oscillator) circuit based on the 
CK3401 op-amp. Component values may be chosen to give any 
specific output frequency required, within limits. The following com- 
ponent values give a 1 kHz square wave output. 
Rl — 10 M ohm 
R2- 3Mohm 
R3- 30 k ohms 
R4-10Mohm 
C-O.Ol^F 

Oscillation frequency will depend on the IC parameter and the 
values of the external resistors. The components shown, the 
output frequency will be 1 kHz and in the form of a square wave. 

The addition of a diode to this circuit, as in Fig. 7.2, provides 
a simple pulse generator circuit where the pulse width can be 
adjusted by using different values for R2. The value of resistor 
R3 governs the actual pulse duration. 

An alternative form of multivibrator is to use two op- amps 
connected as cross-coupled inverting amplifiers, as shown in 
Fig. 7.3. Here the frequency is established by the time constants 
of the RC combination Rl-Cl and R2-C2. Rl and R2 should 
be the same value, and can be anything from Ik ohm to 10k 

73 



in O 




_n n_ 



7.2 An almost identical circuit, with the addition of a diode, can be used 
as a pulse generator. Here the value of R3 determines the pulse 
duration and the value of R2 determines the 'off period. 



I # f * T T ° " ve 

" 2 Q r, D 1' — o 

C.,1 _ 




7,3 Multivibrator circuit based on the n 1.91 I integrated circuit which is 
basically two inverting op-amps. The frequency of oscillation is 
determined by the lime constants of Rl. C2 and R2. CI. Suggested 
component values for working as an audio tone generator are: 

Rl and R2 - I kohm to lOkohm 

CI andC2-0.02fiFto2)jF 

C3 0.01 uF 

C4 100(jF/12 volts 

IC1 and IC2 -Fairrhild ^1.914 (pins2and5 not used) 
Supply voltage 3.6 to 6 volts. 



ohms. CI and C2 should also be similar values, and anything 
from 0.01 to lOfjF can be used. The basic rules governing 
adjustment and oscillation frequency are that for any partic- 
ular value of Rl and R2, increasing the value of CI and C2 will 

74 



MULTIVIBRATORS 

decrease the oscillation frequency, and vice versa. Similarly, 
for any particular value of CI and C2 decreasing the value of 
Rl and R2 will increase the frequency, and vice versa. 

With the component values shown, i.e. Rl — R2 = 8,2k ohms 
and CI = C2 = 0.2fiF, the oscillation frequency will be 1 kHz. 
Decreasing the value of Rl and R2 to 1 k ohm should result in 
an oscillation frequency of 10 kHz. 

A rather more versatile multivibrator circuit is shown in Fig, 
7.4, which has independent controls of 'on' and "off periods. 



_l i diode 







C2 



7.4 Multivibrator circuit with adjustable 'on' and 'off periods. 
Component values: 

Rl-lOOkohms CI -ice text 

R2-100kohms C2-0.01uF 

R3 -lOOkohms 

R4 - ■ 1 Mohm potentiometer 

R5 1 Mohm potentiometer 

R6 2 k ohms 

R7 2kohms 

R8 2 k ohms potent iometer 

1C- CAS 130 

Supply voltage 15 volts 

The frequency range is adjustable by choice of capacitor CI 
which governs the duration of the square wave pulse generated, 
viz: 

Value of CI pulse period 

IjaF 4mintolsec 

O.liiF 0.4minto lOOmin 

O.OlfiF 4mintol0min 

O.OO^iF 4 sec to 1 min 

75 



frequency 

250-1 Hz 

2 500 -600 Hz 

1500 -6 000 Hz 

15000 kHz-60 kHz 



INTEGRATED CIRCUITS 

Adjustment of 'on' and 'off times of oscillation within these 
ranges is governed by the potentiometers R4 and R5. 

Another multivibrator circuit is shown in Fig. 7.5, which is 
particularly notable for its stable performance. The frequency 
of oscillation is maintained to within plus or minus 2 per cent 



fiJament bulb 
or LED with 
ballast resistor 




■Q ►»• 



7.5 Astable multivibrator with low frequency of duration to work a flash- 
ing light. Component values given provide a flashing rate of about 1 
per second working off a 6 to 1 5 volt battery. 

Rl 3Mohms C-QASjiF 

R2 12Mohms 

R3 - ISMohms 

R4-4.3Mohms 

R5-1.2Mohms 
1C-CAS094 

Filament bulb — 6 or 12 volts, depending on battery voltage. 

on any supply voltage from 6 to 15 volts and is independent of 
the actual voltage. It uses a CA3094 op-amp 1C with external 
resistors and one capacitor. The circuit "also includes a lamp 
which flashes on and off at a rate of one flash per second with 
the component values given. 

Flashing rate can be adjusted by altering the values of Rl 
and R2 and/or C. To adjust values to give any required 
flashing rate (frequency), the following formula applies; 



frequency = 



1 



where Rl = 



2RCI n (2Rl/R2 + l) 
RA.RB 



RA + RB 



76 



MULTIVIBRATORS 

In a variation on this circuit shown in Fig. 7.6, the intro- 
duction of a potentiometer R2 enables the pulse length to be 



O ,ve 




-i — ♦■ — • — • 



-O -ve 



7.6 Adjustable multivibrator circuit, potentiometer R2 varying the pulse 
width, or 'on' time of the LED indicator. 

Flashing rate is approximately I per second. Supply voltage required 
for this circuit is 22 to 30 volts. 
Component values: 

Rl - 27kohms 

R2 50kohms potentiometer C — 560 pF 

R3 27k ohms 

R4 lQOkohms 

R5- lQOkohms 

R6- 300 k ohms 

R7 — ballast resistor to suit LED used 

IC-CA309A 

LED — light emitting diode 



varied whilst maintaining a constant frequency (pulse 
repetition rate). Again this circuit can be used to flash a Fila- 
ment lamp, or a light emitting diode. In the latter case, a 
ballast resistor is needed in series with the LED. 

Another straightforward free-running multivibrator is shown 
in Fig. 7.7, using a CA3094 integrated circuit. The frequency is 
controlled by the value selected for R3. and so using a poten- 
tiometer for this component enables the frequency to be 
adjusted. The frequency is also dependent on the supply 
voltage, which can be anything from 3 volts up to 12 volts. 

Designing a multivibrator circuit to work at an audio 
frequency, whilst retaining adjustment of frequency, forms the 

77 



INTEGRATED CIRCUITS 



basis of a metronome. The only additional circuitry required is 
a simple low- power audio amplifier connecting to a loud- 
speaker of the kind described in Chapter 4, 




O - vc 



7.7 Free running multivibrator (or pulse generator) circuit, the frequency 
of which can be varied by adjustment of the potentiometer R4. 
Component values: 

Rl-2.7Mohms 

RS-SSOkohms 

R3- 100 k ohms 

R4 — 5 k or lOkohms potentiometer 
C-0.01uF 

diodes — any silicon diodes 

IC - CA3094 



78 



Chapter Eight 

VOLTAGE REGULATORS 

Where a semiconductor circuit operating on low 
voltage dc is powered from the mains supply via a step-down 
transformer, voltage regulation is highly desirable in many 
circuits in order to ensure constant dc supply voltage. This can 
be provided by using Zener diodes in associated circuitry. 
Exactly the same function can be performed by a single IC. A 
particular advantage is that such an IC can also incorporate 
internal overload and short-circuit protection which would call 
for numerous extra components in a circuit using discrete 
components. 

A typical circuit is shown in Fig. 8.1, giving a rectified, 
positive dc voltage output from the centre tapped secondary of 




-N- 



I 



-►h 



output voltage 
Ci-ve 



smoothing capacitors 



transformer 



8.1 Typical basic circuit for stepping down an ac voltage via a 

transformer and rectifying it to produce a lower voltage dc output, A 
voltage regulating IC is also shown in this circuit. Note that a rectang- 
ular symbol is used for the IC in this case, not a triangle. 



the transformer. The same components can be used in mirror- 
image configuration to give a negative output voltage from the 
centre tap (in which case the polarity of the two electrolytic 
capacitors must be reversed). 

Performance characteristics of a family of ICs designed as 
voltage regulators are given on p. 80. They are quite small 
devices in a TO -39 metal case with three leads — input, output 
and earth— see Fig. 8.2. The earth or ground lead is internally 
connected to the case. 



79 



INTEGRATED CIRCUITS 

IC type no. input 

voltage 
TBA435 20 

TBA 625A 20 

TBA625B 27 

TBA 625C 27 



/ _ 

i > 






L«-7mm »|* 



12.5mm 



— I 




Max. output 
current 

200 mA 
200 mA 
200 mA 

200 mA 

output 
input 



ground 



8.2 






TBA4S5 integrated circuit is enclosed in a TO-39 metal can shape 
and looks like a transistor because it only has three leads. It is a 
complete voltage regulator circuit with internal overload and short 
circuit protection and can be used in the circuit of Fig. 8.1. The 
drawing is approximately twice actual size. 



There are numerous other simple voltage regulators which 
can be built from integrated circuit arrays (see Chapter 2) 
simply by 'tapping' the appropriate leads to connect the indivi- 
dual components required into the complete circuit. An 
example is shown in Fig. 8.4, which is a regulator to provide an 
adjustable constant voltage dc output from an unregulated (and 
thus possibly variable) 20 volt dc input. It uses the transistors, 
diode and Zener diode contained in the CA 3Q97E chip with a 
potentiometer and external resistor to complete the circuit. 
The actual output voltage can be adjusted from 9.5 to 15 volts 
by the setting of the potentiometer, with an output current 
ranging up to 40 mA, depending on the value of the output 
load. 

Other simple voltage regulators can be based on op-amps. A 
basic circuit is shown in Fig. 8.5, The reference voltage is set by 
the Zener diode, the value of Rl being chosen to provide op- 
timum Zener current for the input voltage concerned. The 
(regulated) output voltage is determined by the reference 
voltage (V ref) and the values of R2 and R3: — 



., • r / R2 + R3 \ 

Vout=Vref(-R^) 




out 



8,3 Adjustable output voltage regulator circuit. The potential divider 
formed by R 1 and R2 following the IC enables the output voltage to 
be adjusted via R2; otherwise the circuit is the same as Fig. 8.1. 
Alternatively this circuit can be applied to a dc input: 

Vout = Vl(l+||)+l c R2 

Component values for this circuit with an input voltage of 1 8 volts: 

Rl-680ohms 

R2 — 0-1 SOohms potent iometer 

C -10u.F 

IC-TBA4S5 
Note. Other IC voltage regulators can be used and/or different input 
voltages, in which case different values of Rl and R2 may apply. As a 
general rule R2 needs to be about one-third to one-half the value of 
Rl. 




-C- 



- -■" O 



R3 I 

output 
9,5-15 volts 
regulated 



O-v* 



8.4 Voltage regulator using the CA3097E integrated circuit array. This 
provides 9.5 to 15 volts regulated output from a 20 volts dc input, the 
actual output voltage being determined by the setting or R3. 
Component values: 

Rl 2kohms 

R2 - 2 kohms 

R3 — 2 . 5 kohms potentiometer 

R4-l,5kohms 




out 



•ve O 



8,5 Simple voltage regulator circuit using an op amp and a Zcner diode 
to set the regulated voltage. The values of resistors R2 and R3 deter- 
mine the output voltage (.see text). 

A circuit which provides a small difference between volts in 
and volts out is shown in Fig. 8.6, Using a PNP transistor it 
needs only about 1 volt to saturate the transistor, whilst 
adequate current is available for the regulating circuit using an 
NPN transistor. The same circuit would need about 4 volts 
difference between input and output to maintain regulation. 



PNP transistor 




e.6 



Voltage regulator circuit incorporating a PNP transistor which gives a 
difference between V in and V but of about 1 volt (i.e. the voltage 
necessary to saturate the transistor). 
Component values: 

RI-) 

R2-f seet0 * 1 

R3-10kohms 

R4 - 5 kohms potentiometer 

IC CA3085 

transistor — 40362 (or equivalent) 

Dl . D2 silicon diodes 

82 



CI-2uF 

C2 -O.OluF 



VOLTAGE REGULATORS 
With the circuit shown in Fig. 8.6, 

voltsout = I.6 (Rl + R2 ) 
Rl 

Another very useful circuit is shown in Fig. 8.7, which 
provides a split supply from a single battery source. In other 
words it halves the input voltage whilst also producing a good 
degree of regulation of the two (plus and minus) voltage 
outputs. None of the component values is critical but Rl and 
R2 should be of close-tolerance type of equal value. Input 
voltage can range from 6 to 36 volts, when one half of the input 
voltage will appear between output + and 0, and the other 
between and output - . 




O |v_ 



'out 

8.7 This circuit gives a regulated split supply from any input voltage from 
5 to 36 volts. 
Component vatu<:\: 

Rl — 180 kohms (close tolerance) 

R2 - 180 kohms (close tolerance) 

CI 25uF 

C2 25uF 

TR1 ZN1711 (or equivalent) 

TR2 -40362 (or equivalent) 

IC-CA741 



83 



Chapter Nine 

ELECTRIC MOTOR SPEED CONTROLLERS 

A VARIETY OF ICS are designed as speed regulators for small 
dc motors such as those used in portable cassette players, movie 
cameras, models and toys. The object is to 'govern' the motor so 
that it runs at a constant speed, independent of variations in 
battery supply voltage and load on the motor. The TDA1 151 is 
selected for the following circuits, having a maximum rating of 
20 volts (which covers most model and other small dc motors), 
with an output current of up to 800 milliamps. It is a flat rec- 
tangular plastic package with three leads emerging from one 
end, and comprises 18 transistors, 4 diodes and 7 resistors in a 
linear integrated circuit. 

In its simplest application it is used with a potentiometer (Rs) 
acting as a speed regulation resistance (and by which the actual 
motor speed is adjusted); and a torque control resistor (R t ) 
which provides automatic regulation against load on the 
motor. Both these resistors are bridged by capacitors, although 
C2 can be omitted— see Fig. 9.1 . Component values shown are 
suitable for a 6 to 12 volt supply. 



supply 



X 



— n 1 

1 I — 1 — 



electric 
motor 



9.1 Use of the TDA1 1 51 linear integrated circuit as a speed regulator for 
a small dc electric motor. 
Typical component values: 

R 5 — 1 kohm 

R t -280ohms 

CI — 10mFto2^F ■ 

C2 (if used) 25juF 

84 



ELECTRIC MOTOR SPUED CONTROLLERS 

A slightly different circuit is shown in Fig. 9.2, using a 
TCA600/900 or TCA610/910 integrated circuit. These have 
maximum voltage ratings of 14 and 20 volts respectively; and 
maximum current ratings of 400 milliamps for starting, but 
only 140 milliamps for continuous running. 



f 



■Uppty 
volts 



I 
o- 



ic 



C1 



t 



6 



electric 
•motor 



9.2 Application circuit for the TCA600/610 or TCA900'910 motor speed 
regulators. R, is the speed regulation resistor (variable). R t is the 
torque control resistor. A suitable value for CI is 0. 1 F. A diode can be 
added in line 3 to provide temperature compensation as well. 



Devices of this type work on the principle of providing a 
constant output voltage to the motor independent of variations 
of supply voltage, the value of" this voltage being set by 
adjustment of R. At the same time the device can generate 
a negative output resistance to compensate speed fluctuations 
due to variations in torque. This negative output resistance is 
equal to RT/K, where K is a constant, depending on the 
parameters of the device, viz: 



IC 


K. (typical) 


Vref 


Ic 


TDA1151 


20 


1.2 


1.7mA 


TCA600/900 


8.5 


2.6 


2.6mA 


TCA6 10/910 


8.5 


2.6 


2.6mA 



The above also shows the reference voltage (Vref) and 
quiescent current drain (I ) of the three ICs mentioned. 

85 



INTEGRATED CIRCUITS 

The following relationships then apply for calculating 

suitable component values for these circuits: 

R,= K.Rm 

where Rm is the typical motor resistance 

. rT> Vref.RT 

minimum value of Rs= _ — tt, — 7 — TTTVv 

Eg--(Vref-l RT) 

where Eg= back em/of motor at required or rated speed 

Io= quiescent current drain of the device 

Actual voltage developed across the motor is given by: 

Volts (at motor) = Rm.Im + Eg 

where Im is the current drain by the motor at 

required or rated speed 




IT"** 



^*J -» 






It" 



— k 1 . 



**"j— p*- 




_ 3 

i— • 
1 — 


J 1! 

■ 




1 COB*. 
* — 



9.3 Physical appearance of ihe TCA600/610 in TO -39 metal can and 
TCA900/910 in flat plastic package (TO-126). 




9.4 Although small devices, these integrated circuits for motor speed 
regulation are based on quite complicated circuitry. This diagram 
shows the internal circuits. 



87 



Chapter Ten 

FILTERS 

A BASIC FILTER CIRCUIT consists of a combination of a 
resistor and a capacitor. This combination of R and C has a 
time constant which defines the cut-off frequency of the filter; 
but the actual mode of working also depends on the configur- 
ation of the two components —see Fig. 10.1. 

With R in series and C across the circuit, frequencies lower 




frequency ■ 



frequency ■ 



low- pass filter 



high-pass filter 



10.1 Basic filters are provided by a combination of resistor (R) and 
capacitor (C). A low pass filter attenuates frequencies above the 
critical frequency (f J. A high pass filter attenuates frequencies below 

f c' 
than the cut-off frequency are passed without attenuation. 
Frequencies at above the cut-off frequency are then sharply 
attenuated. This is called a tow- pass filter. 

With C in series and R across the circuit, frequencies above 
the cut-off frequency are passed without attenuations. 
Frequencies below the cut-off frequency are then sharply atten- 
uated. This is called a high- pass fitter. Practical circuits for 
Practical circuits for these two types of filter are shown in Fig. 
10.2. 

The amount of attentuation provided by a filter is expressed 
by the ratio volts out/ volts in, or voltage ratio. This is quoted in 
decibels (dB) — a 3dB drop being equivalent to a voltage ratio 
drop from 1 .0 to 0.707, or a. power loss of 50 percent. 

88 






In 



CH~D-±-{ 



Hl-t 

C1 



out 



R1 R2 



T 

czT 

-± — •- 




— *- -\^ out 



CA301 



<HM-4I 

CI C2 



low-pass filter 







CA741 



nigh-pass filter 

10.2 Basic low-pass and high-pass filter circuits incorporating an op-amp 
for better performance. 

Op-amps can be used as practical filters associated with an 
external capacitor, with the advantage that the more sophisti- 
cated circuitry involved can provide superior performance to 
straightforward Recombinations. 

Two filter circuits based on the CA301 op-amp are shown in 
Fig. 10.2. In the case of the low-pass filter component values 
are calculated from the formula: 

R1 + R2 



Gl = 



C2 = 



1.414RlR2f c 

1.414 



{Rl + R2)f c 
where f c is the effective cut-off point 
In the case of the high-pass filter circuit: 

R1 + R2 



Cl = 



C2 = 



1.732 Rl R2f c 
1.732 



(Rl + R2)f c 

Bandpass filters or bandwith filters can be produced by com- 
bining a low-pass filter in series with a high-pass filter. If the 
band width is from f^ to fn. then the cut-off frequency for the 
low-pass filter is made fu and that of the high-pass filter 
il — Fig. 10.3 (left). This filter combination will pass 
frequencies from ft_ to fu, i.e. in the desired band. 

To produce a band-reject filter, a low -pass filter is used in 
parallel with ahigh-pass filter, as in the second diagram. This 
combination will reject all frequencies within the band ft to fu. 

89 



low 
pass 



high 
pass 





low 
pass 








1 












>- ■ ■■■ (j 




high 
pass 











Bandwidth filter 



band- reject filter 



10.3 A low-pass filter in scries with a high-pass filter passes frequencies only 
within the bandwidth f|. — ft-|. A low pass filter in parallel with a high- 
pass filter rejects all frequencies with the band width fi. - fn. 



Some other practical filter circuits using op-amps are given 
in Figs. 10.4, and 10.5. 



*- output 



input H1 




10.4 A notch filter rejects input signals at a specific centre frequency but 
passes all other frequencies. This is a working circuit, the centre 
frequency being determined by the value of components in the two 
networks RS-R4R5 R6: and C2-C3-C4. The actual 'sharpness' of 
rejection or notch width is adjustable via potentiometer R6. 
Component values for a 1 k Hi centre frequency are: 
Rl-18kohms CI lOfiF 

R2 18kohms C2-0.001u:F 

R3 150kohms CS-O.OOlfiF 

R4 150kohms C4-0.001|/F 

R5-56kohms C5-10/iF 

R6 — SOkohms potentiometer 
IC-CA3035 

90 




Out 



10.5 Simple circuit for a high Q notch filter. Capacitor CI and C2 are 
equal in value. Capacitor C3 = Cl/2. Resistor Rl is twice the value of 
R2 . The centre frequency is 

1 



f c 2ji 



91 



Chapter Eleven 

INTRODUCING DIGITAL CIRCUITS 

The DIGITAL SYSTEM (also known as the binary system) is 
based on counting in l's. Thus it has only two digits (known as 
'bits') - O(zero) and l(one) - which are very easy to manip- 
ulate electronically. It only needs a simple on-off switch, for 
example, to count in this manner. The switch is either 'off 
(showing zero as far as the circuit is concerned) or 'on' (repre- 
senting a count of 1). It can continue to count in l's, or even 
multiply, divide, etc, in association with other simple types of 
switches. The fast-as-light speed at which electronic devices can 
count makes the digital system very suitable for building 
computer circuits, particularly as only a few basic operations 
have to be performed. The fact that these operations, using 
simple logic circuits or gates in suitable combinations, may 
have to be repeated very many times is no problem either. 

The decimal system expresses a number in powers of 10. In 
other words individual digits, depending on their order 
represent the digit value x 10° , digit value x 10 ' , digit value x 
I0 3 , etc, reading from right to left . Putting this the correct way 
round, and taking an actual number— say 124: 

124= Ixl0 3 +2xl0'+4xl0 
= 100 + 20 + 4 
The binary system expresses a number in powers of 2 using 
only the two digits 1 and 0. 

Thus 1011 = lx2 3 +0x2 1 +0x2 l + 1x2° 
= 8 +0 +2 +1 
= 11 
Thus a binary number is longer, written down, than its corres- 
ponding decimal number, and can get very long indeed with 
large decimal numbers (e.g. 10,000 = 1010100010000) but this 
does not matter at all as far as electronics 'counting' is 
concerned. It only makes it difficult for people to convert 
decimal numbers to binary numbers, and vice versa. Here are 
two basic rules. 



92 












INTRODUCING DIGITAL CIRCUITS 

Converting decimal to binary 

Write the decimal number on the right-hand side, divide by 
two and write down the result, placing the remainder (0 or 1) 
underneath this number. Divide the number obtained in the 
top line by 2 and carry the remainder (0 or 1) down to make a 
next step to the left. Repeat this operation, progressing further 
to the left each time, until you are left with an in the top line. 



Example 



















1 


2 


4 


9 


19 decimal 


this is the binary number 


1 








1 


1 


remainder 



Converting binary to decimal 

Write down progressively from right to left as many powers 
of 2 as there are digits in the binary number* . Write the binary 
number underneath. Determine the powers of 2 in each 
column where a 1 appears under the heading and then add all 
these up. 

Example 
Binary number 10101, which has 5 digits, so write down five 
stages of powers of 2 starting with 2° and reading from right to 
left. 

2' 2 3 2 2 2" 
10 10 
16 4 
16 + 4+1 = 21 



Write down binary number 
Convert to decimal 
Add 



2° 

1 

1 



Logic 

Logic systems also work on the binary number process, com- 
monly based on the difference between two dc voltage levels. If 
the more positive voltage signifies 1 , then the system employs 
positive logic. If the more negative voltage signifies 1 , then the 
system employs negative logical should be noted that in both 
cases, although the lower or higher voltage respectively signifies 
0, this is not necessarily a zero voltage level, so the actual 
voltage values have no real significance. 

There is another system , known as pulse -logic, where a 'bit' is 

(*A group of binary digits or 'bits' which has a certain significance, i.e. 
represents a binary number in this case, is often called a 'bite' or 'word'. 

93 



INTEGRATED CIRCUITS 

recognized by the presence or absence of a pulse (positive pulse 
in the case of a positive-logic system and negative pulse in the 
case of a negative-logic system) . 

Gates 

Logic functions are performed by logic gates. The three 
basic logic functions are OR, AND and NOT. All are designed 
to accept two or more input signals and have a single output 
lead. The presence of a signal is signalled by 1 and the absence 
of a signal byO. 

The four possible states of an OR gate with two inputs (A and 
B) are shown in Fig. 11.1. There is an output signal whenever 





B 

11.] The three states of an OR gate. A and B are inputs and Y is the 
output. Note the general symbol used to illustrate a gate. For com- 
pactness a semicircle may be used instead of the symbol shown here 
(e.g. sec Fig. 12.1). 

there is an input signal applied to input A OR input B (and also 
with input at A and B simultaneously). This applies regardless of 
the actual number of inputs the gate is designed to accept. The 
behaviour of an OR gate (again written for only two inputs) is 
expressed by the following trut h table: 



A 


B 


output (Y) 














1 


1 


1 





1 


1 


1 


1 



It can also be expressed in terms of Boolean algebra, calling the 
output Y 

Y = A + B + . + N 

where N is the number of gates 

The important thing to remember is that in Boolean algebra 
the sign + does not mean 'plus' but OR. 

94 









INTRODUCING DIGITAL CIRCUITS 

The AND gate again has two or more inputs and one output, 
but this time the output is 1 only if all the inputs are also 1 . The 

A B Y 



inputs 



A 

o- 



o- 

B 



1 — I \_J 

AND 1 1 

I ^ uutpu 



Y 

-o 

output 












1 











1 





1 


1 


1 



TRUTH TABLE 
1 1 .2 An AND gate and corresponding truth table. 

truth table in this case is quite different — Fig. 11.2. The corres- 
ponding equation of an AND gate is: 

Y = A- B.....N 
or Y = A x B xN 

This time the • or x sign does not mean 'multiplied by' as in 
conventional arithmetic, but AND. 

The NOT gate has a single input and a single output — Fig. 
11.3, with output always opposite to the input, i.e. if A = 1, Y = 




THUTH TABLE 



11.3 



A NOT gate and corresponding truth table. Note the symbol used in 
this case is the same as that for an op-amp or amplifier, and the 
following small circle designates an inverted output . 

and if A «■ 0, Y = 1 . In other words it inverts the sense of the 

output with respect to the input and is thus commonly called an 

inverter. 

Its Boolean equation is: 

Y = A 
(Y equals NOT A) 

Combinations of a NOT gate with an OR gate or AND gate 
produce a NOR and NAND gate, respectively, working in the 
inverse sense to OR and AND. 

Diode-logic (DL) circuits for an OR gate and an AND gate 
are shown in Fig. 11.4. Both are shown for negative logic and 
are identical except for the polarity of the diodes. In fact a 
positive-logic DL or OR gate becomes a negative-logic AND 
gate; and a positive-logic AND gate a negative -logic OR gate. 

95 



AO-CZJ— M- 



-M- 



o-LZZI— M- 



5 



y 
-O 



ao— tZZr— W-i 

bo — cZh- M 



no— IZZHW- 1 



r 5 



1 1 A A Diode Logic (DL) negative logic OR circuit (left ) and a DL negative 
logic AND gate (ngAl)- 

Thc simple NOT gate or inverter shown in Fig. 1 1 .5 is based 
on a transistor logic — an NPN transistor for positive -logic and 
a PNP transistor for negative -logic. The capacitor across the 
input resistance is added to improve the transient response. 

Practical Gates 

Most logic gates are produced in the form of integrated 
circuits, from which various 'family' names are derived. NAND 



^ 1 - 



Uy 



3 



■9 



Y 

-o 



A 

o- 



MZZF 



r 



NPN 
transistor 



-e 



i 



PNP 
tranaiator 



1 1 .5 Transistor Logic {TL) positive logic inverter circuit (left) and a TL 
negative logic NOT circuit (right), 

and NOR gates, for example, are a combination of AND or OR 
gates, respectively, with a NOT gate inverter. From the basic 
circuits just described, such functions can be performed by 
diode-transistor logic or DTL gates. 

Faster and rather better performance can be realized with 
transistor-transistor-logic gates (TTL). During the early 1970's 
DTL and TTL represented the bulk of the IC digital 

96 



INTRODUCING DIGITAL CIRCUITS 

productions, but since then various other IC families have 
appeared, each offering specific advantages and more 
functions for particular applications. These are: 
RTL (resistor-transistor logic) which can be made very 
small— even by microelectronic standards — and is capable of 
performing a large number of functions, 

DCTL (direct-coupled-transistor logic), which employs the 
same type of circuit as RTL but with the base resistors omitted. 
This gate, which can perform NOR or NAND functions, has 
the advantage of needing only one low voltage supply and has 
low-power classification. 

HTL (high threshold logic) is based on diode- transistor logic 
similar to DTL but also incorporates a Zener diode to stabilize 
the circuit and provide high immunity to 'noise'. It is usually 
chosen for applications where this feature is important. 
MOS (metal oxide semiconductor logic), based entirely on Field 
effect transistors (FETs) to the complete exclusion of diodes, 
resistors and capacitors, yielding NAND and NOR gates. 
CMOS (complementary metal -oxide-semiconductor logic) 
using complementary enhancement devices on the same IC 
chip, reducing the power dissipation to very low levels. The 
basic CMOS circuit is a NOT gate (inverter), but more 
complicated NAND and NOR gates and also flip-flops can be 
formed from combinations of smaller circuits (again in a single 
chip). 

ECL (emitter-coupled logic) also known as CML (current- 
mode logic). This family is based on a differential amplifier 
which is basically an anolog device. Nevertheless it has 
important application in digital logic and is the faster 
operating of all the logic families with delay times as low as 
1 nanosecond per gate. 
Flip- Flops 

A flip-flop is a bistable circuit and another important 
element in digital logic. Since it is capable of storing one bit of 
information it is functionally a 1-bit memory unit. Because this 
information is locked or 'latched' in place, a flip-flop is also 
known as a latch. A combination of n flip-flops can thus store 
ann-bit word, such a unit being referred to as a register. 

A basic flip-flop circuit is formed by cross-coupling two 
single -input NOT gates, the output of each gate being 

97 




U.6 1-bit memory or latch circuit obtained by cross-coupling two NOT 
gates (or two single-inrjut NAIMD gates). The output has two^tates 
Y=l, Y = 0: or Y = 0. Y=l. For fhp-flops_the symbols Q and Q, are 
often used for the outputs instead of Y and Y respectively. 

connected back to the input of the other gate — Fig. 11.6, How- 
ever, to be able to preset or clear the state of the flip-flop, two 
two-input NOT gates cross-coupled are necessary, each 
preceded by single- input NOT gates as shown in Fig. 11.7. 



B O 




O v 



11.7 Flip-flop circuit with preset using four NOT gates. S is the set or 
preset input. R is the reset or clear input. 

When the flip-flop is used in a pulsed or clocked system the 
preceding gates are known as the steering gates with the cross - 
coupled two-input gates forming the latch. This particular 
configuration is also known as a S-R or R-S flip-flop. 



Fresot (Pr) 




Ck 



Cr 



11,8 j-K flip-flop circuit (.left) with corresponding symbol (right). 



INTRODUCING DIGITAL CIRCUITS 

Two other variations of the flip-flop are also produced as 
integrated circuits: 

J -K flip-flop — which is an S-R flip-flop preceded by two AND 
gates. This configuration removes any ambiguity in the truth 
table. It can be used as a T-type flip-flop by connecting the J 
and K inputs together (see Fig. 11.8 for connections), 
D-type flip-flop — which is a J-K flip-flop modified by the 
addition of an inverter (see Fig. 11,9). It functions as a 1-bit 
delay device. 



D 

o- 



o- 

Ck 



L4> 



J Pr O 
Ck 



K 



Cr 



Ck 



Cr 3 



11.9 A D-type flip-flop circuit (left) is provided by a J-K flip-flop allied to 
an inverter. The symbol for a D-type flip-flop is shown on the right. 

Fan-in and Fan- out 

The terms/an -m and fan-out are used with IC logic devices. 
Fan-in refers to the number of separate inputs to a logic gate. 
Fan-out is the number of circuit loads the output can 
accommodate, or in other words the number of separate 
outputs provided. Fan-out is commonly 10, meaning that the 
output of the gate can be connected to 10 standard inputs on 
matching gates. Each separate input represents a load, the 
higher the number of separate loads the higher the current 
output of the device providing fan -out needs to be in order to 
provide the standard load on each input, i.e. passing enough 
current to drop each input voltage to the design figure. 

It is possible to increase fan-out by replacing diode(s) with 
transistor(s) in the device concerned, so 10 is by no means a 
maximum number, 

ROM 

ROM stands for read-only memory, a system capable of 
converting one code into another. The best known application 
is to convert the reading of a digital instrument such as an 
electronic calculator into a numerical read-out via an LED 



99 



INTEGRATED CIRCUITS 

(light emitting diode) display. The advantage of a ROM is that 
it is programmable and thus adaptable to different read-out 
systems. It does not follow, however, that it uses the minimum 
number of components to match a particular application. 
Special IC chips designed for a specific application may be 
more economic in this respect, but not necessarily in cost, 
unless there is a very large demand for that particular IC. The 
calculator market is a case in point where a special chip can 
offer advantages over a ROM. 

RAM 

RAM stands for random -access memory and is basically a 
collection of flip-flops or similar devices capable of memorizing 
information in binary form. Information can be written-in or 
read out in a random manner. 

The Shape of Digital ICs 

In physical appearance, most digital ICs look like any other 
dual in-line (or sometimes quad in-line) IC package, or 
ceramic flat packages. They are not readily indentified as 
digital ICs, therefore, (except by type number) although their 
function is quite specific. The more complicated digital ICs 
may, however, have considerably more pins than usual. It is 
also common practice to give pin diagrams which not only 
definethe pinpositionsbut a lsotheirspecificf unction (Fig. 11.10). 



CONNECTION DIAGRAM 



LOGIC DIAGRAM 



«M 




, 


17 




%» 


ABtWC&V IK^Ul 


1*1? | 


2 


11 


]t**f 


ABtmttt IW1 


*DD*E5S iV>ur 


(*S03 | 


I 


to 


|[*1] 


ADOPfSS IHPUT 


A0DHES5 INPUT 


(* III 1 

ic~T> | 


4 
4 


m 
» 


) 


40LWS4 INPUT 


CHIP SELECT 


*DD 


DjiTa INPUT 


tO|l | 


I 


it 


]m t 

] 


CHIP tHMlLf 


o*ta output 


RC 


»ODMf*£ INPUT 


IAQ) | 


I 


it 


](MI 


*QDPE55 INPUT 


looars* input 


lATj | 


I 


i> 


] *i 


ADPHE** 'NP\if 


iDOACSS IPAIT 


t*ll | 


10 
II 


13 
II 


|fA3] 


AOCNESS IMFVT 


*CC 


WJMf OMf 






-. r-< 






'REFRESH A0PQESS A 


). AS 










rrn., 



1 1.10 Example of a Random Access Memory integrated circuit with 
connection diagram (Mullard M340 with a capacity of 4096 'bits'). 
This is in the physical form of a 22 lead dual-in-line package. 



Chapter Twelve 

ELECTRONIC ORGANS 

ONE OF THE MAJOR PROBLEMS in the design of electronic 
organs is the large number of mechanical contacts called for 
using conventional (discrete component) circuitry. With two 
manuals of four octaves each, for example, 98 mechanical 
contacts are needed. This not only complicates construction 
but could also be a source of trouble in operation. There is 
often the limitation that each key is only able to play one note, It 
is desirable for electronic organs to be able to play more than 
one octave-related note per key, increasing the number of 
mechanical contacts required by that factor, e.g. 5 x 98 = 490 
contacts for the example quoted to be able to play five octave- 
related notes per key. 

A number of integrated circuits have been developed, 
usually based on digital logic, to overcome such limitations. 
Many also provide additional features which may be desirable. 
An example is the (Mullard) TDA1008 which consists of a 
matrix of gate circuits with eight divide-by-two gates in each 
circuit. It is a 16-lead dual-in-line plastic package (SOT-38). 

One drive input only is required for delivering nine octave- 
related notes and, by actuating a key input, five successive 
signals out of the nine can be selected and transferred to the 
output. Five key inputs are available, each selecting a different 
combination. Other features which are available are 'sustain' 
and 'percussion' of the output signals; and also 'decay' of 
modulations. 

Further simplification of an electronic organ circuit can also 
be provided by using a top octave synthesizer (TOS) instead of a 
series of master oscillators to derive the twelve top octave 
frequencies required for a 'full' organ. A TOS must be 
associated with a master oscillator capable of generating a 
suitable 'least common multiple' frequency, with the TOS 
following it, then providing the twelve highest notes. Used with 
a suitable gating matrix, further sub-multiples of these notes 
are obtained, e.g. in the case of the TDA1008 the following 

101 



INTEGRATED CIRCUITS 



output frequencies are ava 


lable from the five keys, where f is 


the actual input frequency: 






key 1 key 2 

output 1 f f/2 
output 2 f/2 f/4 
output 3 f/4 f/8 


key 3 

f/4 
f/8 
f/16 


key 4 key 5 
f/8 f/16 
f/16 f/32 
f/32 f/64 


output 4 f/8 f/16 


f/32 


f/64 f/128 


outputs f/16 f/32 


f/64 


f/128 f/256 



This, in effect gives nine different notes available from each 
of twelve available input frequencies from the TOS, or 96 
different notes. Further, operating two or more keys 
simultaneously will give the sum signal of these frequencies. 

Master Oscillator 

A suitable frequency for the master oscillator is about 
4.5 MHz. A variety of circuits can be used providing they have 
suitable stability and the necessary amplitude and slew rate for 
driving the TOS properly. If the master oscillator is a sine wave 
generator, then it will be necessary to follow this with a Schmitt 
trigger to obtain the required slew rate. This is not necessary 
with a square-wave generator and a very simple circuit of this 
latter type based on the NAND gates contained in the HEF401 1 
integrated circuit is shown in Fig. 12,1. This requires a 

Integrated circuit 
I 1 



ai 



i r 




12.1 Master (square- wave) oscillator circuit to feed top octave Synthesizer. 
Components: 

Rl 3k ohms 
R2 -lkohm 
C -27pF 
IC-HER4011 
TUS-AYEG214 



ELECTRONIC ORGANS 

stabilized 12-vo!t supply, as does the TDA1008, so the same 
supply can be used for both the master oscillator and 
TDA1008. 

The master oscillator output connects to the Top Octave 
Synthesizer, the tone outputs of which form the input to the 
TDA1008. They can be directly connected since the input 
signal pin of the TDA1008 has an impedance of at least 
28 k ohms. 

Gate Matrix 

Connections to the TDA1008 integrated circuit are shown in 
Fig. 12.2. The different levels of supply voltage required are 6 



in-.jt 
Q 



keys 



• 6 volts 

o — 



X 



i i i 




16 15 14 13 n 11 10 9 
} TDA1O08 

1 2 3 4 5 6 7 8 



.12 volts 



♦ 9 volts 




to pin 13 



outputs Q1 02 OS 04 OS 
12.2 Basic electronic organ circuit using five keys. Resistors Rl arc all 
Ikohm. Resistors R2 are all IQOkohms. 01. Q2, QS. Q4 and Q5 are 
the tone outputs to feed an audio amplifier circuit with loudspeaker. 

volts, 9 volts and 12 volts, as shown. The five keys can be 
directly connected, although current-limiting resistors can be 
used in each key line if necessary. 

Five different output frequencies are available at each 
output OJ, Q2, Q,3. Q4, Q5, depending on which key is 
activated (see table above). To avoid sub-harmonics being 
generated it is advisable to connect any not-required Qoutputs 
to the + 6 vol t su pply 1 ine . 

103 



INTEGRATED CIRCUITS 
Sustain 

To actuate sustain and percussion effects, a time-delay 
circuit can be added associated with each key, as shown in Fig. 
12,2, This circuit will sustain the tone(s) for a period after 



! 



mm a 




m 13 « ti 

TDA1006 




to pin 13 



12.3 'Sustain' added to ihe circuit of Fig. 12.2. Other components are con- 
nected as before . 
Com.pon.ent values: 

Resistors — 2 .2 M ohms 

Capacitors — 0.5(jF 

R —Series resistors, if required 

release of the key, but with the resistor also providing a certain 
delay time. The addition of a series resistor (RS) will delay the 
build-up of notes, depending on the RC time constant of this 
resistor and the associated capacitor in the circuit. Component 
values given are selected for good tonal response, but this is also 
a matter of personal preference and so some adjustment of 
values may be preferred. It is also possible to shorten the decay 
time of the sustain by adjusting the voltage applied to pin 7. A 
circuit for doing this is shown in Fig. 12.4, 

Percussion 

If percussion is required this can be arranged by connecting 
a capacitor to pin 8 to discharge during keying, associated with 
a series resistor to give a suitable time constant. Using a 0.47 F 

104 



ELECTRONIC ORGANS 



capacitor, a suitable series resistor value can be found by 
experiment. The decay time is also adjustable via the circuit 
shown in Fig. 12.4. 



TDA 1008 










7 


R1 











1 to >6 volts 



1 f diode i 



R2 



diode 2 



12.4 Adjustable voltage to pin 7 for decay control . 
Component values: 

Rl — lOOohms potentiometer 

R2- 100 ohms 

diode 1-BZX75C2V1 

diode2-BOW62 

To retain sustain as well, the circuit shown in Fig. 12.5 
should be used. If sustain is wanted, switch SI is closed and 



TDA 1008 



• 6 volts 





Rl S2p 



R2 



12.5 Percu ssion ci rcu i I wi t h su st ain , connect ing to pi n 8 . 
Component values: 
Resistors 
Rl-lOkohms 
R2-2Mohms 
Capacitors 
Cl-0.47)iF 
C2-0.47(iF 



INTEGRATED CIRCUITS 



switch S2 opened. CI then remains charged to sustain the note 
as long as a key is held down. Once the key is released the note 
will decay at the rate established by the decay circuit connected 
to pin 7, To operate percussion, switch SI is open and switch S2 
closed. 



106 



Chapter Thirteen 
MISCELLANEOUS CIRCUITS 



HI-FI TONE CONTROLS 

Tone controls fitted to domestic radios and equivalent 
circuits are seldom of high quality. This does not usually mat- 
ter for AM reception (which can never be Hi-Fi); but can 
degrade the performance on FM reception. Similar remarks 
apply to the tone controls fitted to lower priced record players 
and tape recorders. 

High quality tone controls generally demand quite complex 
circuits. ICs enable the number of discrete components 
required to be substantially reduced and, at the same time, 
offer other advantages such as a high input impedance which 
matches a typical high impedance source. Tone control can 
also be combined with audio amplification in IC circuits. 

Fig. 13.1 shows a complete circuit based around a TCA8305 
integrated circuit incorporating a feedback network which 
attenuates the low frequencies and boosts the high frequencies. 
At the same time high frequencies can be attenuated by the 
treble control potentiometer at the input. The volume control, 
also on the input side, provides 'loudness control' at both high 
and low frequencies to compensate for the loss of sensitivity of 
the human ear to such frequencies (i.e. both high and low 
frequencies tend to sound 'less loud' to the ear). 

A simpler circuit, using the same IC, is shown in Fig. 13.2, 
This has a single tone control potentiometer. The circuit 
provides flat response at middle frequencies (i.e. around 
1 kHz), with marked boost and cut of up to ± 10 decibels at 
110Hz and 10kHz respectively in the extreme position of the 
potentiometer. 

A (Baxandall) Hi-Fi tone control circuit associated with 
another type of op-amp is shown in Fig. 13.3. The IC in this 
case is the CA3140 BiMOS op-amp. The tone control circuit is 
conventional and only few additional discrete components are 
required to complete the amplifier circuit around the IC. This 
circuit is capable of ± 15 decibels bass and treble boost and cut 

107 



*vo supply voltage 

o — 



m 



C3 ZZ C4 



in 



Ri 



CI 



U£ 



R2 




fl ff f f 

4 i A • -• — •--•-• •- 



13.1 Hi-Fi tone control circuit suitable for receivers, record players and 
tape recorders and charatcrized by a high input impedance. Potentio- 
meter Rl is the treble control. Potentiometer R9 is the bass control. 
Potentiometer R4 is the volume control. 
Component values: 



R 1 -47k ohms log pot 


CI- 47nF 


R2 lOkohms 


C2- 820 pF 


R3 — l.Bkohms 


CS- lOOfiF 


R4—1 00k ohms log pot 


C4- 0.1 fiF 


R5-100ohms 


05- 100nF 


R6— 15 ohms 


C6- 250 uF 


R7 — 470 ohms- 


C7- IGOuF 


R8- 470 ohms 


C8- lOOpF 


R9-25kohmsiogpot 


C9- 0.33(iF 


RIO- 1 ohm 


C10- 0.22^F 




CH- 0.1 ^F 


IC-TCA8S05 


C12- lOOQuF 



at 100 Hz and 10 kHz respectively. 

An alternative circuit using the same IC and giving a similar 
performance is s^own in Fig, 13.4. Both of these circuits 
require a supply voltage of 30-32 volts. Fig. 13.5 shows the same 
two circuits modified for dual supplies. 

LED DISPLAY BRIGHTNESS CONTROL (Fig, 13.6, page 113) 

How well an LED shows up is dependent on the ambient light 
falling on it. In dim light the display is usually quite bright. In 

108 






+ vG supply voltage 

o- 




13.2 Alternative Hi-Fi tone control circuit 
frequency feedback. Potentiometer Rl 
iometer R7 is the treble control and 
control. 
Component mlues: 

Rl — lOOkohms log pot 
R2- 100 ohms 
R3— ISohrns 
R4- 180 ohms 
R5-27ohms 
R6 — 1 ohm 
R7 — lOkohms log pot 
R8- 150 ohms 
R9-3S0ohms 
R10 lOkohms log pot 
Rll ISohms 
IC-TCA8305 



with separate high and low 
is the volume control. Potent- 
potentiometer R10 the bass 



CI- O.lnF 

C2-- I00^F 

C3- lOOuF 

C4- 500uF 

C5- lOO^F 

C6- 82 pF 

C7 - lGOOnF 

C8 O.lnF 

C9- 0.15^F 

C10 2jjF 

Cll- I piF 

C12 - 2.2uF 



direct sunlight it may be difficult to see at all. The circuit shown 
in Fig. 13.6 provides an automatic brightness control of a 
(single) LED by using a silicon photodiode to sense the amount 
of ambient light and feed a proportional signal to the TCA315 
opamp integrated circuit. As the intensity oflight increases the 
output current from the op-amp increases in proportion, and 
vice versa, thus automatically compensating the brightness of 
the LED for artifical light in an inverse manner. The brighter 
the ambient light the brighter the LED glows, and vice versa. 

109 



O *ve 



1 "LJ" ' 




O-utCHjt 




-O *ve supply 



Output 

f *— 



C5 



P^T 11 



mr 



§-czJ-i==r-Icn— * > 



C7 



R5 R6 



R7 



*"^T 



13.3 Simple Hi-Fi tone control circuit. Component values are determined 

for a supply voltage of 32 volts. Potentiometer R2 is the bass control. 

Potentiometer R5 is the treble control. Components within the dashed 

outline comprise the tone control network. 

Component values: 

Rl- 240 k ohms Cl-750pF 

R2-5Mohmlogpot C2-750pF 

R3- 240 k ohms C3- 20 pF 

R4-51kohms C4-0.1fiF 

R5 5 M ohm linear pot C5-0.1fiF 

R6 — 51kohms Coupling Capacitor 

R7-2.2Mohm (C8) -0.047pF 

R8- 2.2 M ohms 

R9- 2.2 M ohms 

IC-CAS140 



The potentiometer (R6) is used for setting up the circuit 
initially. With a 2.5 volt supply, and with the photodiode in 
complete darkness, R6 should be adjusted to give a current 
reading of about lOOuA (0. 1 milliamps), using a meter in one 
battery lead to check. With this adjustment, and the type of 
photodiode specified, the LED will then receive an impressed 
current of 5 mA per 1000 lux illumination of the photodiode. 
Components: 

Integrated circuit TCA315 op-amp 
Photodiode BPW32 

110 






I 



13.4 



Another Hi-Fi tone control circuit. Potentiometer R4 is the treble 

control. Potentiometer R6 is the bass control. Supply voltage is 30 

volts. 

Component values: 

Rl- 5.1 M ohms 

R2- 2.2 M ohms 

R3-18kohms 

R4— 200k ohms linear pot 

R5-10kohms 

R6 — 1 Mohm log pot 

R7-100kohms 

IC-CA3140 

IC-CA3140 



Cl- 


- O.luF 


C2- 


- 0.01 uF 


C3- 


- 100 pF 


C4- 


- lOOpF 


C5- 


-O.OOl^F 


C6- 


2(iF 


C7- 


-O.Q02(jF 


C8- 


-O.OOauF 



LED LD30 {or equivalent) 

Resistors: Rl 47 kohrn 

R2 47 k ohm 

R3 220 ohm 

R4 47 ohm 

R5 10 Mohm 

R6 250 k ohm potentiometer 

LEDRADIOTUNINGSCALE(Fig. 13.7, page 114) 

This simple circuit displays the tuned frequency of a radio in 
terms of spots of light instead of {or in addition to) the usual 
pointer moving over a scale. An array of 16 LEDs should be 
sufficient to indicate station positions with suitable accuracy 

111 













3 














tc 

C2 




\_/ 




tone 
control 
network 








O tf 






7 




v 1 I 




— 


2 






r 


3 


















T 


■ C3 










X 









supply 

ve 



13.5 



Tone control for dual supplies. The lone control network is the same 
as that in the dotted outline of Fig. 13.3. Supply voltage is 15 volts. 
Component i«ilues: 

CI -0.047nF 

C2 -Q.l^F 

CS -O.lnF 

1C CA3140 



over a typical medium frequency waveband (i.e. 520 kHz to 
1600 kHz). The display is driven by a Siemens UAA170 
integrated circuit. A phototransistor is also used to match the 
brightness of the display automatically to ambient light 
intensity, i.e. dimming the display in dull light and brightening 
the display to make it clearly visible in sunlight. 

The complete ci-xuit is shown in Fig. 13.7. The UAA170 is 
controlled via the voltage divider formed by Rl and R2 
supplying the tuning voltage for the AM tuning diode incorp- 
orated in the IC. Since this diode has non-linear 
characteristics, stations on the left (lower frequency) end of the 
tuning scale will be more closely concentrated, consistent with 
station spacing on this broadcast band . 

The circuit will work on most normal transistor radio supply 
voltages (i.e.Vs = 10 to 18 volts), and with an input voltage for 
frequency indication of Vs ■ 1.2 to 27 volts using two(Siemens) 
LD468 LF.D-arrays. Voltage at the divider point between Rl 
and R2 should be between 0.06 and 1.16 volts and can be 
adjusted by Rl if necessary. The actual brightness of the 

112 




_ve 



13.1 Circuit for automatic control of brightness or an LED using a photo- 
diode to sense the level of illumination. 



display is automatically controlled by the phototransistor 
BP101/1 , and is also adjustable via the 1 kohm potentiometer. 

CAR THIEF ALARM (Fig. 13.8, page 115) 

This is another circuit originated by Siemens and based 
around their TDB0556 A dual timer IC. The first timing circuit 
of this device is used as a bistable multivibrator with the circuit 
activated by switch SI . Output level remains at zero, set by the 
voltage applied to the threshold input pin 2 until one of the 
alarm contact switches is closed causing CI to discharge. 

"Press-for-ofF alarm switches can be fitted to the doors, bon- 
net and boot lid, so arranged that opening of a door or lid 
completes that switch contact. This will produce an output 
signal held for about 8 seconds, pulling in the relay after an 
initial delay of about 4 seconds. The horn circuit is completed 
by the relay contacts so the horn will sound for 8 seconds. After 
this the relay will drop out (shutting off the horn) until capac- 
itor CI charges up again. This will take about 3 seconds, when 
the relay will pull in once more and the horn will sound again. 
This varying signal of 8 seconds horn on, 3 seconds horn off, 
will be repeated until switch SI is turned off (or the battery is 
flattened). This type of alarm signal commands more attention 
than a continuous sounding alarm such as can be given by 
straightforward on-off electrical switching. 

113 



VAA170 




•"• 



1 i 9 ' 



#-#-♦ 



*-4-* 



two LD466 displays 



] 3.7 Sixteen I.ED display to replace or augment the usual pointer and scale 
indication of tuned frequency on an AM radio receiver. 
Component values: 

Rl-330kohms 

R2 - I kohm potentiometer 

R3-6.8kohms 

R4-2.7kohms 

R5 — lOkohms potentiometer 

R6 -470oWms 

ICA UAA170 

photo transistor BP101/1 

LED - two LD468 displays 

The complete circuit is shown in Fig. 13.8 with suitable com- 
ponent values, wired in to appropriate points on a car electrical 
system . 

INTERCOM 

The TCA830S is a powerful, inexpensive op-amp IC which 
makes it a particularly attractive choice for intercoms since the 
circuit can be built with a minimum number of components. 
Many other op-amps do not produce the power required for 
loudspeaker operation without the addition of a further stage 
of transistor amplification. The basic circuit is contained at the 
main' station when the 'distant' station merely comprises a 

114 




- 
Q 
h 



= E 
■ « 

|J 

— c 
k - 

j5 e 

a s 

<~ o 

a-s 

« K 
£ £ 

- ™ 
E I 

I % 

tl 

M S 

? ~ 

■3 < 

y if) 



30 
00 



INTEGRATED CIRCUITS 

loudspeaker and a 'calling' switch. The two stations are con- 
nected by a 3 -wire flex. 

The circuit is shown Fig. 13.9. The TCA830S requires a heat 
sink and is fitted with tabs. A printed circuit is recommended, 




main station 

13.9 Intercom circuit using the TCA830S integrated circuit. This IC is 
powerful enough to operate fairly large loudspeakers. Component 
values are given in the text. 

incorporating two 1 in. (25mm) squares of copper to which the 
IC tabs can be soldered for the heat sink. Component 
positioning is not critical since the circuit handles only audio 
frequencies. 

The transformer (T) has a 50:1 turns ratio and is used as a 
step-down transformer between the IC and speaker(s) — also 
working as a step-up transformer between speaker(s) and IC for 
working in the reverse mode. In other words the transformer 
coil with the larger number of turns is connected to pin 8 on the 
IC, Instead of purchasing this transformer ready-made it can 
be wound on a stack of standard transformer core laminates 
0.35mm thick, giving a core cross-section of 22.5mm 2 . 
Windings arc 600 turns of 0.2mm (36s.w.g.) and 300 turns of 
0.06mm (46s. w.g.) enamelled copper wire. 

The purpose of the transformer is to enable standard 4 to 16 
ohm loudspeakers to be used both as microphones and 
speakers. These speakers can be of any size, bearing in mind 

• 116 



MISCELLANEOUS CIRCUITS 

that the maximum power output of the circuit is of the order of 
2 watts on a 12-voIt supply. The intercom circuit will work on 
any battery voltage down to 6 volts, 9 or 12 volts being recom- 
mended for general operation. 

Components: 

(SGS - ATES) TCA8305 integrated circuit 

Resistors Rl 20kohms 

R2 29ohms 
Capacitors CI -lOOfiF electrolytic 3V 
C2 O.ImF 

C3 1000uFelectrolyticl2V 

Transformer (T) 50:1 turns ratio, power rating 5W. 
Loudspeaker 4 ohms (preferred) 
Switch SI : press break/make 

S2: press make/break 



ICE WARNING INDICATOR 

This very simple circuit uses a thermistor as a temperature 
sensor together with three CA340 IE op-amps and a minimum 
of external components. The operating point of the circuit is 
set by the potentiometer (R2) so that, at an ambient air temp- 
erature approaching freezing point, the light emitting diode 
(LED) starts to flash. As the temperature falls the rate of 
flashing increases until the LED glows continuously once 
freezing point is reached. Accurate calibration can be carried 
out in the freezer compartment of a domestic refrigerator with 
the door open, in conjunction with a thermometer. 

The complete circuit is shown in Fig. 13.10. IC1, IC2 and 
IC3 are separate op-amp circuits contained in the IC. Thus 
pins 1 and 6 are the input to IC1 and pin 5 the output of 1C1; 
pins 11 and 12 the input to IC2 and pin 10 the output of IC2; 
and pins 2 and 3 the input to IC3 and pin 4 the output of IC3. 
Pins 8, 9 and 13 are ignored. Pin 7 connects to the earth side of 
the circuit; and pin 14 to battery plus side. 

Layout of this circuit is not critical but all component leads 
should be kept as short as possible and the LED located some 
distance away from the integrated circuit. This circuit is 
powered by a 12 volt battery. 

117 



■#— O * ve 1 2 volts 




13.30 Circuit for an ice-warning indicator. Adjustment of potentiometer R2 
can set the circuit to flash the LED as air temperature approaches 
freer ing point, with LED staying permanently alight once freezing 
temperature is reached. 



Component values: 
Rl-33kohms 
R2-20kohm 

potentiometer 
R3-150kohms 
R4— 3 M ohms 
R5— 3 M ohms 
R6-30kohms 
R7-3Mohms 
RS-lOMohms 
R9 lOMohms 



IC1. IC2.IC3 CA3401E 
LED- light emitting diode 
Thermistor — Mullard 
VA1066S (or equivalent) 



DIGITAL VOLTMETER 

A digital voltmeter {known as a DVM) has several advantages 
over a conventional pointer-and-needle meter, for example: 

1 . Easier reading with direct presentation of reading in digits. 

2. Greater accuracy and highspeed of reading. 

3. Higher sensitivity. 

4. Greater resolution. 

Unfortunately the circuitry required for a DVM is quite com- 
plicated, making it much more expensive than its simple 

118 



MISCELLANEOUS CIRCUITS 

analog counterpart in the form of moving coil instrument. 
However, by using ICs the necessary circuitry for a DVM can be 
simplified and miniaturized and is within the scope of the 
amateur to build. The following design by Siemens avoids the 
use of expensive components and its performance is 
comparable with that of ready-made DVMs in the medium- 
price range (well over £100!). It has a basic range of up to 9.9 
volts with an accuracy of better than 99 per cent . 

The complete circuit is shown in Fig. 13.11. The input 
voltage is converted to a proportional frequency by the op-amp 
TBA221 connected as an integrating amplifier and the 
following monostablc multivibrator TDB556A (IC2). The 
resulting output pulse (at pin 5 of IC2) is determined by the 
time constant of R4 and C4 and is of the order of l.S^s. This 
pulse turns transistor Tl 'on' and "off, the multivibrator thus 
supplying pulses to the clock input of the counter SAJ341 with a 
repetition frequency proportional to the input voltage. 

These pulses are counted during a measuring interval 
defined by the other half of the astable multivibrator 
TDB556A (IC1) with a duty cycle of < 0.5. Its output directly 
controls the blocking input of the counter (SAJ341). At the 
beginning of each measuring interval, 5AJ341 is reset to Q,\, 
Qp. Of;, Qp = L (corresponding to decimal 0) by a short Im- 
pulse applied to the reset input IR. This reset pulse is produced 
by the measuring-interval generator, the inverting transistor 
T2 and the following differentiation circuit. 

The display, which can be extended to four digits, operates 
on a time-multiplex basis using a level converter (TCA671), 
decoder (FLL121 V) and display driving transistors BC307 and 
BC327. 

The circuit is set up using a known input voltage (preferably 
between 2 and 3 volts). Potentiometer Rl is then adjusted to 
show the correct reading on the display. If this is not possible 
then the value of resistor R2 should be changed for the next 
nearest value up or down, i.e. 270 or 180 kilohms as found 
appropriate (one value will make matters worse, the other 
better). 

The circuit needs two separate power supplies of +5 volts at 
300 milliamps and -12 volts at 200 milliamps. For accurate 
working of the meter both supply voltages should be regulated. 

119 




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MISCELLANEOUS CIRCUITS 

Components: 

IC1 &IC2- Siemens TDB0556 A 

Siemens TBA221 integrating op-amp 

Siemens SAJ341 universal converter 

Siemens TCA671 level converter 

Siemens FLL1 21V decoder 

Note: all the above are integrated circuits. 

HA1101 seven-sequence LED display 

Capacitor and resistor values are shown on the circuit diagram . 

Diode and transistor type numbers are shown on the circuit 

diagram . 

INFRA-RED TRANSMITTER AND RECEIVER 

There are three practical possibilities for remote control sig- 
nalling: radio (as in model radio control systems); ultrasonics; 
and light transmission. The latter is the simplest in terms of 
components and circuitry, especially where simple on/off com- 
mand only is required. It can be extended to more channels, 
but at the expense of more complicated circuitry. 

Using infra-red light transmission it is possible to achieve a 
range of 100 feet (30 metres) or more quite readily in normal 
ambient light. Even greater range is possible if the transmitter 
light beam is focused by a simple lens system. Such infra-red 
remote control systems have become highly practical with the 
appearance of high-efficiency LEDs with a high infra-red 
transmission and suitable photodiodes which can be used as 
detectors in receivers. As with other remote control systems the 
basic units involved are a transmitter and receiver. 

Single-channel infra -red transmitter 

This circuit uses the Siemens GoAs improved light-emitting 
diode LD241 in a pulse modulated transmitter circuit involving 
the use of two oscillators, a sub -carrier frequency of 50 kHz 
modulated by a frequency of 10 Hz, the second oscillator 
having a duty cycle of 250:1 . These circuits are based around 
four CMOS N AND-gates (available in a single IC). The LED is 
square-wave modulated by a Darlington pair of NPN 
transistors. 

The complete transmitter circuit is shown in Fig. 13.12 and 
is quite straightforward. Despite drawing a peak current of 1 

121 



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BC 339 (« 

13.12 Design for an infra-red transmitter (Siemens), Component values are 
shown on the diagram, hut a complete specification for the active 
components is: 

IC1. 1C2. IC3. 1C4 - 4 x CMON NAND-gates type (Siemens) 
HEF4011P 

Transistors — BC238/25 (or equivalent) 
LED - Siemens LD27 
diode-BAY61 



amp the average current drain is only 2mA with a 6-voIt 
battery supply, the peak current actually being supplied from 
the 470ftF capacitor. This is possible since the 5kHz output 
pulse train has a duration of only 400fis in a repetition period of 
100 ms. 

Single channel Infra -red Receiver. 

By comparison the receiver circuit is more complex since it 
employs six discrete transistor plus a Darlington pair in 
addition to three NAND-gates Fig. 13.13. The detector is a 
BPW34 photodiode matched to an input impedance of 
80k ohms at 50kHz, Signals are received in the form of an 
infra-red pulse train from the transmitter. The receiver circuit 
following the photodiode amplifies, clips and rectifies the pulse 
train signal and applies it to a monostable multivibrator which 
covers the space between two pulse trains. This means that a tic 
voltage is available at the output of the receiver as long as the 
transmitter signal is held on. This receiver output can be used 
to operate a relay, simple escapement or a signalling light (e.g. 
a filament bulb or LED). 

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Since ambient light will introduce a 'noise' voltage in the 
diode or interference, the circuit is intended for narrow band 
working which operates by placing an infra-red filter in front of 
the photodiode. This can be an infra-red photographic filter, 
or a section of unexposed but developed colour film (e.g. Agfa 
CT18). The transmitter- receiver combination should then 
work satisfactorily in ambient light intensities up to 10000 lux 
with fluorescent light, 4000 in sunlight, or 500 lux maximum 
in the case of filament lighting. 

A simpler receiver circuit is shown in Fig. 13.14 but will only 
be suitable for working in dull ambient light (less than 500 lux). 



ELECTRONIC REV COUNTER 

The (Mullard) SAK140 is an integrated circuit designed as a 
revolution counter for car engines, etc. Connected to the 
contact breaker it is fed by input pulses at 'engine speed' rate 
and converts these pulses into output current pulses of constant 
duration and amplitude. The output pulse duration is 
determined by an external Resistor — Capacitor network. By 
suitable choice of R and C, the pulse 'count' can be indicated 
on any milliameter. The circuit will also work on any supply 
voltage between 10 and 18 volts (e.g. from a car's 12-volt bat- 
tery) and performance is independent of actual supply voltage 
(or variation in supply voltage). 

The complete circuit is shown in Fig. 13.15. Resistor Rl is 
selected so that the input current does not exceed 10 mA (a 
suitable value for 12-volts supply is 15kohms, when typical 
input current will be 5mA). The diode acts as a voltage 
regulator to prevent overloading by large input pulses. 

The peak output current is determined by the value of R2 
plus R3. This should be at least 50 ohms, the actual value being 
chosen to suit the range of the milliameter used. If R2 is made 
50 ohms, then R3 can be made 1 kohm, say, and adjusted to 
suit the range of the milliameter. 

The output pulse duration is determined by the combination 
of R4 and C2. Suitable values can be found by experiment, the 
suggested starting point being: 

R4-270kohms 

C2-10nF 



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Component values: 

Resistors Capacitors 

Rl-15kohms Cl-220nF 

R2-50ohms C2-* 

R3-lkohms C3 - lOOnF 

R4-* 

R5-27ohms 

IC-SAK140 "wetext 

QUARTZ CRYSTAL CLOCK 

The (Milliard) SAA1114 is a CMOS integrated circuit 
designed to work as the 'heart' of a crystal controlled clock 
powered by a single battery. It comprises a master 4 MHz oscil- 
lator, a 22-stage frequency divider and a driver for a unipolar 
stepper motor. With a crystal frequency of 4, 1943 MHz, the 
output is in the form of a 1 Hz (1 second) pulse of 31 .25 milli- 
seconds duration. 

A complete clock circuit is shown in 13.16 and requires only 
a few external components. The quartz crystal is a critical com- 
ponent and is associated with a trimmer capacitor CI for time 
adjustment. Maximum supply voltage is 3 volts, the circuit 
drawing a current of about 50A and supplying a motor output 
current of about 50mA. 

Another version of this particular IC is also available which 
incorporates an alarm circuit triggered by an alarm switch 
operated by the clock hand movement. Output of this alarm 

126 



13.16 Crystal controlled clock circuit . 
Component values: 

CI -22pF trimmer capacitor (type 2222 808 32409) 

C2-22pF 

C3-22pF 

Xtal-4. 1 943 MH?. (type no. 4322 143 03111) 

IC-SAAU14 



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13.17 Additional alarm facility provided in 1CSAA1 114:2 via pins 5 and 6. 

from pins 5 to 6 is a 250 Hz tone signal operating for 4 seconds 
when the alarm is triggered. External connections for this 
alarm circuit are shown in Fig. 13.17, the clock motor circuit 
being as in Fig. 13.16. 



127 









INDEX 






INDEX 



Adders, 31 
AGC. 64 

Alarm circuit, 127 
Am pi i ficr , 32 , 44 el seq . 
v\i Radio. 66, 107 
Anti-log amplifier, 36 
Arrays, 22 ct scq. 
Area, heat sink. 61, 62 
Astable multivibrator, 27, 76, 77, 

119 
Attenuation. 88 

Band -pass filters, 89 
Band -reject filters, 89 
Bandwidth fillers, 90 
Baxandall tone control, 107 
Bias current. 43 
Binary system. 92 
Binary to decimal. 93 
Bit. 93, 97 
Boolean algebra, 94 
Bridge amplifiers, 59 
Buffer. 32 

Capacitance booster, 41 

Capacitors, 17 

Car thief alarm, 113 

Cascade, 45 

Chip. 13.44,58 

Circuits, see separate list, pages 7 to 

9 
cmos, 97 

Common-mode rejection ratio, 42 
Component density, 14 
Constant current source;'28 
Constant voltage source, 29 
Converters, 37 
Copper area, 61 
Crystal earpiece, 18, 65 
Current source, 38 



Current-to-voltage converter. 37 

Darlington pair. 121, 122 
DCTI., 97 
Decay. 104 
Decimal to binary, 93 
Decoupling capacitor, 64 
Differentia! amplifier, 35 
Differentiator, 34 
Digital circuits, 92etseq. 
Digital system. 92 
Digital volt meter. 1 18 
Diode-logic. 95 
Diodes, 15, 23.26. 80 

DTL. 96 

D-type flip-flop. 99 
Dual-in-line, 20, 44 

ECL, 97 

Electric motor speed controllers, 84 

et seq. 
Electronic organs, 101 et seq. 
Electronic rev counter, 124 

Kan -in, 99 

Fan -out, 99 

Filters. 41, 88 et scq. 

Flat packages, 20 

Flip-flops, 97 ct seq. 

FM radio, 66. 107 

Free-running multivibrator, 77, 78 



Gain, 45 et seq. 
Gale matrix. 101. 
Gates. 94 



103 



Heat sink, 17. 44. 50. 54. 55, 60 et 

seq,, 1 16 
Hi-Fi amplifiers, 54 et seq. 
Hi-Fi tone controls, 107 et scq. 
High pass filter, 41,42.88 



131 






INDEX 



High power amplifier, 57 
High -Q notch filter, 91 
HTL, 97 
Hybrid itfs, IS 
Hysteresis. 40 

Ice warning indicator, 117 

IC holders, 21 

Inductors, 17 

Infra-red receiver, 121, 122 

Infra-red transmitter, 121 

Integrated circuit outlines. 19 

Integrator. 33 

Intercom, 114 

Inverting terminal, 30 

J-K flip-flop, 99 

Large scale integration (LSI), 14 

Latch, 97, 98 

LED, 108, 109. Ill etseq., 114. 117 

Linear integrated circuits, 30 

Log amplifier, 35 

Logic, 93 etseq. 

Logic gates. 94 

Log multiplier, 36 

Loudspeaker. 49. 66, 78. 116.117 

Low pass filter. 41,42,88 

Master oscillator. 101, 102 

Medium scale integration (MSI), 14 

Metronome, 78 

Microelectronic technology, 13 

Monolithic IC's, 15 

mos, 17, 97 

M os capacitor, 17 

Multiplier. 32 

Multivibrator, 38, 73 et seq. 

Negative logic, 93 
Non-inverting terminal, 30 
Non -polarized capacitors, 17 
Notch filter, 90 

Offset current, 43 
Offset voltage, 43 
OP-amps, 30 et seq . 



Open-loop gain, 42 
Oscillation, 74 

Package shapes, IC's, 20 

Percussion, 104 

Phase inverter, 32 

Photo etching, 13 

Photo diode, 110 

Photo transistor, 1 12 

Polarized capacitors, 17 

Positive logic, 93 

Power, 60 

Power supply rejection ratio, 42 

Pre- amplifier, 65 

Printed circuit, 17, 60. 71. 72 

Putsegenerator, 73 

Pulse-logic. 93 

Quad in-line, 20, 44, 49, 54 
Quartz crystal clock, 126 
Quiescent current drain, 60, 85 

Radio circuit. 64 et seq. 
Radio receiver, 48 

RAM, 100 

Receiver, infra-red, 121, 122 
Regenerative comparator, 39 
Register, 97 
Regulation, 84 
Resistors. 16 
Rev counter, 1 24 
ROM, 99 
rtl, 97 

St hm in trigger, 39 

Short circuit protection, 51 

Slew rate, 43 

Small scale integration (SSI), 14 

Smoothing capacitors, 79 

Speed controllers, 84 etseq. 

Square wave generator, 102 

S-R flip-flop. 99 

Steering gates, 98 

Stereo amplifiers, 54 et seq. 

Stripe resistors, 16 

Sub-harmonics, 103 

Subtracter, 33 



INDEX 



Super- alpha pair, 27 
Sustain, 104 

Temperature coefficient, 17 
Thermal shutdown. 53 
Thin -film resistors, 16 
Tone controls, 107 et seq. 
Top octave synthesizer ,101 
Transformers, 17, 116 
Transistor outlines, 20 
Transistors, 13, 15. 23. 24. 26. 35. 

80 
Transmitter, infra-red, 121 
Triggering, 40 
Trip voltage, 39 



Truth table, 94, 95 
ttl, 96. 97 
Tuned circuits, 64 

Veroboard.20 
Voltage follower, 36 
Voltage regulator, 79 et seq. 
Voltage-to-current converter, 37 

Wafer, 13. 14 

Working circuits, see separate lists 
pages. 7 to 9 

Zener diode. 22. 29, 79. 80 



132 



133 






(continued from front flap) 

voltage regulators to complete radios and 
electronic organs. Many other useful pro- 
jects are also included, like a car thief 
alarm; ice warning indicator; filters and 
Hi-Fi tone controls; pulse generators; 
infra-red transmitter and receiver; elec- 
tronic rev counter; quartz crystal clock; 
and many, many more. It will prove, 
therefore, a vital book for anyone interes- 
ted in, or in any way concerned with, 
modern electronics practice. 



Companion volume in this series : 

CLOCKS and CLOCK REPAIRING 
by Eric Smith 

Ii may come as something of a surprise to find thai 
cleaning and repairing clocks makes an extremely 
rewarding hobby to anyone who has the aptitude 
and patience. Without guidance and some of ihe 
proper tools, however, the novice can all too 
easily do great harm. 

This book clearly sets out the tools and materials 
required for practical working on clocks. It is 
copiously illustrated with photographs and line 
drawings, and there is an extensive glossary of 
terms. The book should prove an invaluable 
introduction to a craft which can be of absorbing 
interest and pleasure, and one which is being 
increasingly explored by amateurs. 







The publishers would tike to thank Mullards 
for their kind co-operation in providing material 
for the jacket photographs. 



LUTTERWORTH PRESS 










mo